diff --git a/src/tap/db/JDBCConnection.java b/src/tap/db/JDBCConnection.java
index 02ef467248230c3d94f83e02b831c22faedf7cd1..a109ed11982e6126913cc31de7aa64fec140524c 100644
--- a/src/tap/db/JDBCConnection.java
+++ b/src/tap/db/JDBCConnection.java
@@ -53,6 +53,7 @@ import tap.data.ResultSetTableIterator;
 import tap.data.TableIterator;
 import tap.log.TAPLog;
 import tap.metadata.TAPColumn;
+import tap.metadata.TAPCoosys;
 import tap.metadata.TAPForeignKey;
 import tap.metadata.TAPMetadata;
 import tap.metadata.TAPMetadata.STDSchema;
@@ -939,10 +940,18 @@ public class JDBCConnection implements DBConnection {
 				logger.logDB(LogLevel.INFO, this, "LOAD_TAP_SCHEMA", "Loading TAP_SCHEMA.tables.", null);
 			List<TAPTable> lstTables = loadTables(tap_schema.getTable(STDTable.TABLES.label), metadata, stmt);
 
+			// load all coordinate systems from TAP_SCHEMA.coosys: [non standard]
+			Map<String, TAPCoosys> mapCoosys = null;
+			if (isTableExisting(tap_schema.getDBName(), STDTable.COOSYS.label, stmt.getConnection().getMetaData())){
+				if (logger != null)
+					logger.logDB(LogLevel.INFO, this, "LOAD_TAP_SCHEMA", "Loading TAP_SCHEMA.coosys.", null);
+				mapCoosys = loadCoosys(tap_schema.getTable(STDTable.COOSYS.label), metadata, stmt);
+			}
+
 			// load all columns from TAP_SCHEMA.columns:
 			if (logger != null)
 				logger.logDB(LogLevel.INFO, this, "LOAD_TAP_SCHEMA", "Loading TAP_SCHEMA.columns.", null);
-			loadColumns(tap_schema.getTable(STDTable.COLUMNS.label), lstTables, stmt);
+			loadColumns(tap_schema.getTable(STDTable.COLUMNS.label), lstTables, mapCoosys, stmt);
 
 			// load all foreign keys from TAP_SCHEMA.keys and TAP_SCHEMA.key_columns:
 			if (logger != null)
@@ -1147,6 +1156,62 @@ public class JDBCConnection implements DBConnection {
 			close(rs);
 		}
 	}
+	
+	/**
+	 * Load all coordinate systems declared in the TAP_SCHEMA.
+	 * 
+	 * @param tableDef		Definition of the table TAP_SCHEMA.coosys.
+	 * @param metadata		Metadata in which the found coordinate systems will be inserted (see {@link TAPMetadata#addCoosys(TAPCoosys)}).
+	 * @param stmt			Statement to use in order to interact with the database.
+	 * 
+	 * @return	A map containing all declared coordinate systems (key=coosys ID, value={@link TAPCoosys}).
+	 *        	<i>note: this map is required by {@link #loadColumns(TAPTable, List, Map, Statement)}.</i>
+	 * 
+	 * @throws DBException	If any error occurs while interacting with the database.
+	 * 
+	 * @since 2.1
+	 */
+	protected Map<String, TAPCoosys> loadCoosys(final TAPTable tableDef, final TAPMetadata metadata, final Statement stmt) throws DBException{
+		ResultSet rs = null;
+		try{
+			// Build the SQL query:
+			StringBuffer sqlBuf = new StringBuffer("SELECT ");
+			sqlBuf.append(translator.getColumnName(tableDef.getColumn("id")));
+			sqlBuf.append(", ").append(translator.getColumnName(tableDef.getColumn("system")));
+			sqlBuf.append(", ").append(translator.getColumnName(tableDef.getColumn("equinox")));
+			sqlBuf.append(", ").append(translator.getColumnName(tableDef.getColumn("epoch")));
+			sqlBuf.append(" FROM ").append(translator.getTableName(tableDef, supportsSchema));
+			sqlBuf.append(" ORDER BY 1,2,3,4");
+
+			// Execute the query:
+			rs = stmt.executeQuery(sqlBuf.toString());
+
+			// Create all coosys:
+			HashMap<String, TAPCoosys> mapCoosys = new HashMap<String, TAPCoosys>();
+			while(rs.next()){
+				String coosysId = rs.getString(1),
+						system = rs.getString(2), equinox = rs.getString(3),
+						epoch = rs.getString(4);
+
+				// create the new coosys:
+				TAPCoosys newCoosys = new TAPCoosys(coosysId, system, nullifyIfNeeded(equinox), nullifyIfNeeded(epoch));
+				
+				// create and add the new coosys:
+				metadata.addCoosys(newCoosys);
+				mapCoosys.put(coosysId, newCoosys);
+			}
+
+			return mapCoosys;
+		}catch(SQLException se){
+			if (!isCancelled() && logger != null)
+				logger.logDB(LogLevel.ERROR, this, "LOAD_TAP_SCHEMA", "Impossible to load coordinate systems from TAP_SCHEMA.coosys!", se);
+			throw new DBException("Impossible to load coordinate systems from TAP_SCHEMA.coosys!", se);
+		}finally{
+			close(rs);
+		}
+	}
+	
+
 
 	/**
 	 * <p>Load into the corresponding tables all columns listed in TAP_SCHEMA.columns.</p>
@@ -1166,8 +1231,38 @@ public class JDBCConnection implements DBConnection {
 	 * @param stmt			Statement to use in order to interact with the database.
 	 *
 	 * @throws DBException	If a table can not be found, or if any other error occurs while interacting with the database.
+	 * 
+	 * @deprecated	This method is now replaced by {@link #loadColumns(TAPTable, List, Map, Statement)} which has an additional parameter:
+	 *            	the list of declared coordinate systems. 
 	 */
+	@Deprecated
 	protected void loadColumns(final TAPTable tableDef, final List<TAPTable> lstTables, final Statement stmt) throws DBException{
+		loadColumns(tableDef, lstTables, null, stmt);
+	}
+
+	/**
+	 * <p>Load into the corresponding tables all columns listed in TAP_SCHEMA.columns.</p>
+	 * 
+	 * <p><i>Note:
+	 * 	Tables are searched in the given list by their ADQL name and case sensitively.
+	 * 	If they can not be found a {@link DBException} is thrown.
+	 * </i></p>
+	 * 
+	 * <p><i>Note 2:
+	 * 	If the column column_index exists, column entries are retrieved ordered by ascending table_name, then column_index, and finally column_name.
+	 * 	If this column does not exist, column entries are retrieved ordered by ascending table_name and then column_name.
+	 * </i></p>
+	 * 
+	 * @param tableDef		Definition of the table TAP_SCHEMA.columns.
+	 * @param lstTables		List of all published tables (= all tables listed in TAP_SCHEMA.tables).
+	 * @param mapCoosys		List of all published coordinate systems (= all coordinates systems listed in TAP_SCHEMA.coosys).
+	 * @param stmt			Statement to use in order to interact with the database.
+	 * 
+	 * @throws DBException	If a table can not be found, or if any other error occurs while interacting with the database.
+	 * 
+	 * @since 2.1
+	 */
+	protected void loadColumns(final TAPTable tableDef, final List<TAPTable> lstTables, final Map<String, TAPCoosys> mapCoosys, final Statement stmt) throws DBException{
 		ResultSet rs = null;
 		try{
 			// Determine whether the dbName column exists:
@@ -1179,6 +1274,9 @@ public class JDBCConnection implements DBConnection {
 			// Determine whether the columnIndex column exists:
 			boolean hasColumnIndex = isColumnExisting(tableDef.getDBSchemaName(), tableDef.getDBName(), "column_index", connection.getMetaData());
 
+			// Determine whether the coosys_id column exists:
+			boolean hasCoosys = (mapCoosys != null) && isColumnExisting(tableDef.getDBSchemaName(), tableDef.getDBName(), "coosys_id", connection.getMetaData());
+
 			// Build the SQL query:
 			StringBuffer sqlBuf = new StringBuffer("SELECT ");
 			sqlBuf.append(translator.getColumnName(tableDef.getColumn("table_name")));
@@ -1201,6 +1299,8 @@ public class JDBCConnection implements DBConnection {
 				sqlBuf.append(", ");
 				translator.appendIdentifier(sqlBuf, DB_NAME_COLUMN, IdentifierField.COLUMN);
 			}
+			if (hasCoosys)
+				sqlBuf.append(", ").append(translator.getColumnName(tableDef.getColumn("coosys_id")));
 			sqlBuf.append(" FROM ").append(translator.getTableName(tableDef, supportsSchema));
 			if (hasColumnIndex)
 				sqlBuf.append(" ORDER BY 1,12,2");
@@ -1254,6 +1354,21 @@ public class JDBCConnection implements DBConnection {
 				newColumn.setStd(std);
 				newColumn.setDBName(dbName);
 				newColumn.setIndex(colIndex);
+				
+				// set the coordinate system if any is specified:
+				if (hasCoosys){
+					int indCoosys = 12; 
+					if (hasColumnIndex)
+						indCoosys++;
+					if (hasDBName)
+						indCoosys++;
+					String coosysId = rs.getString(indCoosys);
+					if (coosysId != null){
+						newColumn.setCoosys(mapCoosys.get(coosysId));
+						if (logger != null && newColumn.getCoosys() == null)
+							logger.logDB(LogLevel.WARNING, this, "LOAD_TAP_SCHEMA", "No coordinate system for the column \""+columnName+"\"! Cause: unknown coordinate system: \""+coosysId+"\".", null);
+					}
+				}
 
 				// add the new column inside its corresponding table:
 				table.addColumn(newColumn);
diff --git a/src/tap/formatter/VOTableFormat.java b/src/tap/formatter/VOTableFormat.java
index 37c185bd14183000575d94d1f590d980a7f039eb..ccee023a839175f51337f6b4ab23856b0af9c106 100644
--- a/src/tap/formatter/VOTableFormat.java
+++ b/src/tap/formatter/VOTableFormat.java
@@ -25,6 +25,7 @@ import java.io.IOException;
 import java.io.OutputStream;
 import java.io.OutputStreamWriter;
 import java.io.PrintWriter;
+import java.util.HashSet;
 import java.util.Iterator;
 import java.util.Map;
 
@@ -35,16 +36,17 @@ import tap.data.DataReadException;
 import tap.data.TableIterator;
 import tap.error.DefaultTAPErrorWriter;
 import tap.metadata.TAPColumn;
+import tap.metadata.TAPCoosys;
 import tap.metadata.VotType;
 import tap.metadata.VotType.VotDatatype;
 import uk.ac.starlink.table.AbstractStarTable;
 import uk.ac.starlink.table.ColumnInfo;
-import uk.ac.starlink.table.DefaultValueInfo;
 import uk.ac.starlink.table.DescribedValue;
 import uk.ac.starlink.table.RowSequence;
 import uk.ac.starlink.table.StarTable;
 import uk.ac.starlink.votable.DataFormat;
 import uk.ac.starlink.votable.VOSerializer;
+import uk.ac.starlink.votable.VOStarTable;
 import uk.ac.starlink.votable.VOTableVersion;
 import adql.db.DBColumn;
 import adql.db.DBType;
@@ -403,12 +405,31 @@ public class VOTableFormat implements OutputFormat {
 			out.write("<INFO name=\"QUERY\"" + VOSerializer.formatAttribute("value", adqlQuery) + "/>");
 			out.newLine();
 		}
-
-		/* TODO Add somewhere in the table header the different Coordinate Systems used in this result!
-		 * 2 ways to do so:
-		 * 	1/ COOSYS (deprecated from VOTable 1.2, but soon un-deprecated)
-		 * 	2/ a GROUP item with the STC expression of the coordinate system. 
-		 */
+		
+		// Insert the definition of all used coordinate systems:
+		HashSet<String> insertedCoosys = new HashSet<String>(10);
+		for(DBColumn col : execReport.resultingColumns){
+			// ignore columns with no coossys:
+			if (col instanceof TAPColumn && ((TAPColumn)col).getCoosys() != null){
+				// get its coosys:
+				TAPCoosys coosys = ((TAPColumn)col).getCoosys();
+				// insert the coosys definition ONLY if not already done because of another column:
+				if (!insertedCoosys.contains(coosys.getId())){
+					// write the VOTable serialization of this coordinate system definition:
+					out.write("<COOSYS"+VOSerializer.formatAttribute("ID", coosys.getId()));
+					if (coosys.getSystem() != null)
+						out.write(VOSerializer.formatAttribute("system", coosys.getSystem()));
+					if (coosys.getEquinox() != null)
+						out.write(VOSerializer.formatAttribute("equinox", coosys.getEquinox()));
+					if (coosys.getEpoch() != null)
+						out.write(VOSerializer.formatAttribute("epoch", coosys.getEpoch()));
+					out.write(" />");
+					out.newLine();
+					// remember this coosys has already been written:
+					insertedCoosys.add(coosys.getId());
+				}
+			}
+		}
 
 		out.flush();
 	}
@@ -502,12 +523,16 @@ public class VOTableFormat implements OutputFormat {
 
 		// Set the XType (if any):
 		if (votType.xtype != null)
-			colInfo.setAuxDatum(new DescribedValue(new DefaultValueInfo("xtype", String.class, "VOTable xtype attribute"), votType.xtype));
+			colInfo.setAuxDatum(new DescribedValue(VOStarTable.XTYPE_INFO, votType.xtype));
 
 		// Set the additional information: unit, UCD and UType:
 		colInfo.setUnitString(tapCol.getUnit());
 		colInfo.setUCD(tapCol.getUcd());
 		colInfo.setUtype(tapCol.getUtype());
+		
+		// Set the coosys ref (if any):
+		if (tapCol.getCoosys() != null)
+			colInfo.setAuxDatum(new DescribedValue(VOStarTable.REF_INFO, tapCol.getCoosys().getId()));
 
 		return colInfo;
 	}
diff --git a/src/tap/metadata/TAPColumn.java b/src/tap/metadata/TAPColumn.java
index 4dbb7433f704ba11fee8bbf4672d6b65299aa075..936909f0340d824fdfe90512e75ca070bb1730bb 100644
--- a/src/tap/metadata/TAPColumn.java
+++ b/src/tap/metadata/TAPColumn.java
@@ -16,7 +16,7 @@ package tap.metadata;
  * You should have received a copy of the GNU Lesser General Public License
  * along with TAPLibrary.  If not, see <http://www.gnu.org/licenses/>.
  * 
- * Copyright 2012-2016 - UDS/Centre de Données astronomiques de Strasbourg (CDS),
+ * Copyright 2012-2017 - UDS/Centre de Données astronomiques de Strasbourg (CDS),
  *                       Astronomisches Rechen Institut (ARI)
  */
 
@@ -69,7 +69,7 @@ import adql.db.DBType.DBDatatype;
  * </p>
  * 
  * @author Gr&eacute;gory Mantelet (CDS;ARI)
- * @version 2.1 (07/2016)
+ * @version 2.1 (07/2017)
  */
 public class TAPColumn implements DBColumn {
 
@@ -132,6 +132,11 @@ public class TAPColumn implements DBColumn {
 	 * <i>Note: Standard TAP column field since TAP 1.1.</i>
 	 * @since 2.1 */
 	private int index = -1;
+	
+	/** Coordinate system used by this column values.
+	 * <i>Note: Of course, this attribute has to be set only on coordinate columns.</i>
+	 * @since 2.1 */
+	private TAPCoosys coosys = null;
 
 	/** Let add some information in addition of the ones of the TAP protocol.
 	 * <i>Note: This object can be anything: an {@link Integer}, a {@link String}, a {@link Map}, a {@link List}, ...
@@ -770,6 +775,28 @@ public class TAPColumn implements DBColumn {
 		this.index = columnIndex;
 	}
 
+	/**
+	 * Get the used coordinate system.
+	 * 
+	 * @return	Its coordinate system.
+	 * 
+	 * @since 2.1
+	 */
+	public final TAPCoosys getCoosys(){
+		return coosys;
+	}
+
+	/**
+	 * Set the the coordinate system to use.
+	 * 
+	 * @param newCoosys	Its new coordinate system.
+	 * 
+	 * @since 2.1
+	 */
+	public final void setCoosys(final TAPCoosys newCoosys){
+		this.coosys = newCoosys;
+	}
+
 	/**
 	 * <p>Get the other (piece of) information associated with this column.</p>
 	 * 
diff --git a/src/tap/metadata/TAPCoosys.java b/src/tap/metadata/TAPCoosys.java
new file mode 100644
index 0000000000000000000000000000000000000000..90e8a63892136204656bf4621b299576cee4ca4c
--- /dev/null
+++ b/src/tap/metadata/TAPCoosys.java
@@ -0,0 +1,175 @@
+package tap.metadata;
+
+/*
+ * This file is part of TAPLibrary.
+ * 
+ * TAPLibrary is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * TAPLibrary is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with TAPLibrary.  If not, see <http://www.gnu.org/licenses/>.
+ * 
+ * Copyright 2017 - Astronomisches Rechen Institut (ARI)
+ */
+
+/**
+ * Definition of a coordinate system.
+ * 
+ * <p>
+ * 	This object just annotates a {@link TAPColumn} object (see {@link TAPColumn#getCoosys()}
+ * 	and {@link TAPColumn#setCoosys(TAPCoosys)}). Its only purpose is to enrich the VOTable
+ * 	metadata so that VO clients (like Aladin and TOPCAT) can use the coordinates the most
+ * 	precisely as possible.
+ * </p>
+ * 
+ * @author Gr&eacute;gory Mantelet (ARI)
+ * @version 2.1 (07/2017)
+ * @since 2.1
+ */
+public class TAPCoosys {
+
+	/** ID of this coordinate system definition.
+	 * <p>It is particularly used in the VOTable to associate columns with it.</p>
+	 * <i>Note: This attribute can NOT be NULL.</i> */
+	protected final String id;
+	
+	/** Name of the coordinate system.
+	 * <p>
+	 * 	It should be a value among:
+	 * 	"ICRS", "eq FK5", "eq FK4", "ecl FK4", "ecl FK5",
+	 * 	"galactic", "supergalactic", "barycentric", "geo app"
+	 * 	and a user-defined "xy" value.
+	 * </p> */
+	protected final String system;
+	
+	/** Equinox of this coordinate system.
+	 * <p>
+	 * 	This parameter required to fix the equatorial or ecliptic systems
+	 * 	(as e.g. "J2000" as the default "eq FK5" or "B1950" as the default "eq FK4").
+	 * </p> */
+	protected String equinox;
+	
+	/** Epoch at which the coordinates were measured. */
+	protected String epoch;
+	
+	/**
+	 * Create a minimum coordinate system definition.
+	 * 
+	 * @param id		ID of the definition to create. <i>(must NOT be NULL)</i>
+	 * @param system	Coordinate system. <i>(must NOT be NULL)</i>
+	 * 
+	 * @throws NullPointerException	If any of the given parameters is NULL or an empty string.
+	 */
+	public TAPCoosys(final String id, final String system) throws NullPointerException {
+		this(id, system, null, null);
+	}
+	
+	/**
+	 * Create a coordinate system definition.
+	 * 
+	 * <p>
+	 * 	Only the ID and the system are required.
+	 * 	The equinox and especially the epoch are optional.
+	 * </p>
+	 * 
+	 * @param id		ID of the definition to create. <i>(must NOT be NULL)</i>
+	 * @param system	Coordinate system. <i>(must NOT be NULL)</i>
+	 * @param equinox	Equinox of this coordinate system.
+	 * @param epoch		Epoch at which the coordinates were measured.
+	 * 
+	 * @throws NullPointerException	If the ID or the system is NULL or an empty string.
+	 */
+	public TAPCoosys(final String id, final String system, final String equinox, final String epoch) throws NullPointerException {
+		if (id == null || id.trim().length() == 0)
+			throw new NullPointerException("Missing Coosys ID!");
+		this.id = id;
+		
+		if (system == null || system.trim().length() == 0)
+			throw new NullPointerException("Missing coordinate system!");
+		this.system = system;
+		
+		this.equinox = equinox;
+		this.epoch = epoch;
+	}
+
+	/**
+	 * Get the ID of this coordinate system definition.
+	 * 
+	 * @return	Its ID. <i>(can NOT be NULL)</i>
+	 */
+	public final String getId() {
+		return id;
+	}
+
+	/**
+	 * Get the coordinate system of this definition.
+	 * 
+	 * @return	Its system. <i>(can NOT be NULL)</i>
+	 */
+	public final String getSystem() {
+		return system;
+	}
+
+	/**
+	 * Get the equinox of this coordinate system.
+	 * 
+	 * @return	Its equinox. <i>(may be NULL)</i>
+	 */
+	public final String getEquinox() {
+		return equinox;
+	}
+
+	/**
+	 * Set the equinox of this coordinate system.
+	 * 
+	 * @param equinox	Its new equinox. <i>(may be NULL)</i>
+	 */
+	public void setEquinox(final String equinox) {
+		this.equinox = equinox;
+	}
+
+	/**
+	 * Get the epoch at which the coordinates were measured.
+	 * 
+	 * @return	Its equinox. <i>(may be NULL)</i>
+	 */
+	public final String getEpoch() {
+		return epoch;
+	}
+
+	/**
+	 * Set the epoch at which the coordinates were measured.
+	 * 
+	 * @param epoch	Its new epoch. <i>(may be NULL)</i>
+	 */
+	public void setEpoch(final String epoch) {
+		this.epoch = epoch;
+	}
+	
+	@Override
+	public int hashCode() {
+		return id.hashCode();
+	}
+
+	@Override
+	public boolean equals(Object obj){
+		if (!(obj instanceof TAPCoosys))
+			return false;
+
+		TAPCoosys coosys = (TAPCoosys)obj;
+		return coosys.getId().equals(getId());
+	}
+
+	@Override
+	public String toString(){
+		return id;
+	}
+	
+}
diff --git a/src/tap/metadata/TAPMetadata.java b/src/tap/metadata/TAPMetadata.java
index d5672674c75e253c3595ec8771f35b27d66fea68..0858031b650918afc710fbaf77277b2624ba6dc0 100644
--- a/src/tap/metadata/TAPMetadata.java
+++ b/src/tap/metadata/TAPMetadata.java
@@ -23,6 +23,7 @@ package tap.metadata;
 import java.io.IOException;
 import java.io.PrintWriter;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.Iterator;
 import java.util.LinkedHashMap;
 import java.util.List;
@@ -75,6 +76,10 @@ public class TAPMetadata implements Iterable<TAPSchema>, VOSIResource, TAPResour
 
 	/** List of all schemas available through the TAP service. */
 	protected final Map<String,TAPSchema> schemas;
+	
+	/** List of all coordinate systems used by columns published in the TAP_SCHEMA.
+	 * @since 2.1 */
+	protected final Map<String, TAPCoosys> coordinateSystems;
 
 	/** Part of the TAP URI which identify this TAP resource.
 	 * By default, it is the resource name ; so here, the corresponding TAP URI would be: "/tables". */
@@ -108,6 +113,7 @@ public class TAPMetadata implements Iterable<TAPSchema>, VOSIResource, TAPResour
 	 */
 	public TAPMetadata(){
 		schemas = new LinkedHashMap<String,TAPSchema>();
+		coordinateSystems = new HashMap<String, TAPCoosys>();
 	}
 
 	/**
@@ -424,6 +430,60 @@ public class TAPMetadata implements Iterable<TAPSchema>, VOSIResource, TAPResour
 			nbTables += s.getNbTables();
 		return nbTables;
 	}
+	
+	/**
+	 * Get the coordinate system definition associated with the given ID.
+	 * 
+	 * @param coosysId	ID of the coordinate system to get. <i>(case sensitive)</i>
+	 * 
+	 * @return	The corresponding coordinate system definition,
+	 *        	or NULL if no match for the given ID.
+	 * 
+	 * @since 2.1
+	 */
+	public TAPCoosys getCoosys(final String coosysId) {
+		return (coosysId == null ? null : coordinateSystems.get(coosysId));
+	}
+	
+	/**
+	 * Add the given coordinate system definition.
+	 * 
+	 * <p><b>Important:</b>
+	 * 	If a coordinate system with the same ID (case sensitive) is already declared in
+	 * 	this {@link TAPMetadata}, it will be replaced by the given one. The replaced
+	 * 	coordinate system is returned by this function.
+	 * </p>
+	 * 
+	 * @param newCoosys	The coordinate system definition to add.
+	 * 
+	 * @return	The coordinate system definition previously declared with the same ID in this {@link TAPMetadata},
+	 *        	or NULL if no coord. sys. was declared with this ID.  
+	 * 
+	 * @since 2.1
+	 */
+	public TAPCoosys addCoosys(final TAPCoosys newCoosys) {
+		if (newCoosys == null)
+			return null;
+		else{
+			TAPCoosys formerValue = coordinateSystems.get(newCoosys.getId());
+			coordinateSystems.put(newCoosys.getId(), newCoosys);
+			return formerValue;
+		}
+	}
+	
+	/**
+	 * Remove the coordinate system declared with the given ID.
+	 * 
+	 * @param coosysId	The ID of the coordinate system definition to remove.
+	 * 
+	 * @return	The removed coordinate system definition,
+	 *        	or NULL if none is declared with the given ID.
+	 * 
+	 * @since 2.1
+	 */
+	public TAPCoosys removeCoosys(final String coosysId){
+		return (coosysId == null) ? null : coordinateSystems.remove(coosysId);
+	}
 
 	/**
 	 * Let iterating over the list of all tables contained in a given {@link TAPMetadata} object.
@@ -871,6 +931,14 @@ public class TAPMetadata implements Iterable<TAPSchema>, VOSIResource, TAPResour
 				tables.addColumn("utype", new DBType(DBDatatype.VARCHAR), "UTYPE if table corresponds to a data model", null, null, null, false, false, true);
 				return tables;
 
+			case COOSYS:
+				TAPTable coosys = new TAPTable(STDSchema.TAPSCHEMA + "." + STDTable.COOSYS, TableType.table, "List of coordinate systems published used this TAP service.", null);
+				coosys.addColumn("id", new DBType(DBDatatype.VARCHAR), "ID of the coordinate system definition.", null, null, null, true, true, false);
+				coosys.addColumn("system", new DBType(DBDatatype.VARCHAR), "The coordinate system (among \"ICRS\", \"eq_FK5\", \"eq_FK4\", \"ecl_FK4\", \"ecl_FK5\", \"galactic\", \"supergalactic\").", null, null, null, false, false, false);
+				coosys.addColumn("equinox", new DBType(DBDatatype.VARCHAR), "Required to fix the equatorial or ecliptic systems (as e.g. \"J2000\" as the default \"eq_FK5\" or \"B1950\" as the default \"eq_FK4\").", null, null, null, false, false, false);
+				coosys.addColumn("epoch", new DBType(DBDatatype.VARCHAR), "Epoch of the positions (if necessary).", null, null, null, false, false, false);
+				return coosys;
+
 			case COLUMNS:
 				TAPTable columns = new TAPTable(STDSchema.TAPSCHEMA + "." + STDTable.COLUMNS, TableType.table, "List of columns of all tables listed in TAP_SCHEMA.TABLES and published in this TAP service.", null);
 				columns.addColumn("column_index", new DBType(DBDatatype.INTEGER), "this index is used to recommend column ordering for clients", null, null, null, false, false, true);
@@ -886,6 +954,7 @@ public class TAPMetadata implements Iterable<TAPSchema>, VOSIResource, TAPResour
 				columns.addColumn("indexed", new DBType(DBDatatype.INTEGER), "an indexed column; 1 means true, 0 means false", null, null, null, false, false, true);
 				columns.addColumn("principal", new DBType(DBDatatype.INTEGER), "a principal column; 1 means true, 0 means false", null, null, null, false, false, true);
 				columns.addColumn("std", new DBType(DBDatatype.INTEGER), "a standard column; 1 means true, 0 means false", null, null, null, false, false, true);
+				columns.addColumn("coosys_id", new DBType(DBDatatype.VARCHAR), "ID of the used coordinate systems (if any).", null, null, null, false, false, false);
 				return columns;
 
 			case KEYS:
@@ -962,11 +1031,18 @@ public class TAPMetadata implements Iterable<TAPSchema>, VOSIResource, TAPResour
 	 * Enumeration of all tables of TAP_SCHEMA.
 	 * 
 	 * @author Gr&eacute;gory Mantelet (ARI)
-	 * @version 2.0 (07/2014)
+	 * @version 2.1 (07/2017)
 	 * @since 2.0
 	 */
 	public enum STDTable{
-		SCHEMAS("schemas"), TABLES("tables"), COLUMNS("columns"), KEYS("keys"), KEY_COLUMNS("key_columns");
+		SCHEMAS("schemas"),
+		TABLES("tables"),
+		COLUMNS("columns"),
+		KEYS("keys"),
+		KEY_COLUMNS("key_columns"),
+		/** Non standard table but anyway expected by this library in order to associated coordinate columns with a coordinate system.
+		 * @since 2.1 */
+		COOSYS("coosys");
 
 		/** Real name of the table. */
 		public final String label;
diff --git a/src/tap/metadata/tap_coosys.html b/src/tap/metadata/tap_coosys.html
new file mode 100644
index 0000000000000000000000000000000000000000..1446eb0d70ea95f5623d45c06aa203fb9cf07e3e
--- /dev/null
+++ b/src/tap/metadata/tap_coosys.html
@@ -0,0 +1,89 @@
+<!DOCTYPE html>
+<html>
+	<head>
+		<meta charset="UTF-8">
+		<title>Coordinate system in TAP metadata</title>
+	</head>
+	<body>
+		<h1>How to declare coordinate system(s) in TAP metadata?</h1>
+		<p>
+			The TAP-1.0 standard does not define any way to convey the
+			coordinate system used by coordinate columns. However, this is
+			more and more required by recent catalogs using recent epoch
+			(e.g. 2015 for Gaia-DR1) or coordinate systems not expected by
+			default by most of the VO applications (e.g. something different
+			from ICRS J2000).
+		</p>
+		
+		<p>
+			In order to provide most accurate metadata as possible, the
+			TAPLibrary gives a way to specify the coordinate system of your
+			coordinates. Here is how to proceed in function of how you provide
+			your TAP metadata:
+		</p>
+		
+		<h3>In <code>TAP_SCHEMA</code></h3>
+		<p>
+			You must add a table in <code>TAP_SCHEMA</code>:
+			<code>coosys</code>. This table must have the following columns:
+		</p>
+		<ul>
+			<li><code>id</code>: VARCHAR <i>(ID of the coordinate system
+				definition as it must be in the VOTable)</i></li>
+			<li><code>system</code>: VARCHAR <i>(The coordinate system among:
+				<code>ICRS</code>, <code>eq_FK5</code>, <code>eq_FK4</code>,
+				<code>ecl_FK4</code>, <code>ecl_FK5</code>,
+				<code>galactic</code>, <code>supergalactic</code>)</i></li>
+			<li><code>equinox</code>: VARCHAR <i>(Required to fix the equatorial
+				or ecliptic systems (as e.g. <code>J2000</code> as the default
+				for <code>eq_FK5</code> or <code>B1950</code> as the default
+				for <code>eq_FK4</code>))</i></li>
+			<li><code>epoch</code>: VARCHAR <i>(Epoch of the positions
+				(if necessary))</i></li>
+		</ul>
+		<p>
+			Then, you need an additional column in
+			<code>TAP_SCHEMA.columns</code>:
+		</p>
+		<ul>
+			<li><code>coosys_id</code>: VARCHAR <i>(ID of the used coordinate
+				systems (if any))</i></li>
+		</ul>
+		<p>
+			Now, all you have to do, is add any coordinate system you need in
+			<code>TAP_SCHEMA.coosys</code> and set the appropriate coordinate
+			system ID in the column <code>coosys_id</code> of all columns using
+			one. Refresh the metadata of your TAP service and now a
+			<code>COOSSYS</code> item should be in the metadata part of your
+			VOTable results (only when there are coordinates with a specified
+			coordinate system).
+		</p>
+		
+		<h3>In an XML file</h3>
+		<p>
+			Unfortunately, the XML definition of the node <code>column</code>
+			does not provide any standard way to provide something as complex
+			as a coordinate system. So, either you keep not providing coordinate
+			systems in your TAP service, or you choose a different method of
+			metadata declaration.
+		</p>
+		<p><i>Tip:
+			Starting your TAP service with an XML file as way to provide
+			metadata will immediately create and initialize correctly the
+			<code>TAP_SCHEMA</code> schema in your database. So, if you want
+			to provide coordinate system information, all you have to do, is to
+			switch the metadata declaration method in order to use this newly
+			created <code>TAP_SCHEMA</code>. Then, just follow the steps listed
+			above for this method.
+		</i></p>
+		
+		<h3>Programmatically</h3>
+		<p>
+			To add a coordinate system to a column, you just have to use the
+			new function of <code>TAPColumn</code>:
+			<code>setCoosys(TAPCoosys)</code>. As in the
+			<code>TAP_SCHEMA</code> method, you can use the same
+			<code>TAPCoosys</code> object for several columns.
+		</p>
+	</body>
+</html>
\ No newline at end of file