Index: src/ooxml/java/org/apache/poi/xssf/usermodel/XSSFWorkbook.java
===================================================================
--- src/ooxml/java/org/apache/poi/xssf/usermodel/XSSFWorkbook.java	(.../https://svn.apache.org/repos/asf/poi/branches/ooxml)	(revision 699004)
+++ src/ooxml/java/org/apache/poi/xssf/usermodel/XSSFWorkbook.java	(working copy)
@@ -337,6 +337,18 @@
     	return null;
     }
 
+    /**
+     * Convenience method to get the active sheet.  The active sheet is is the sheet
+     * which is currently displayed when the workbook is viewed in Excel.
+     * 'Selected' sheet(s) is a distinct concept.
+     */
+    public int getActiveSheet() {
+        //activeTab (Active Sheet Index) Specifies an unsignedInt 
+        //that contains the index to the active sheet in this book view.
+        Long index = workbook.getBookViews().getWorkbookViewArray(0).getActiveTab();
+        return index.intValue();
+    }
+
     public List getAllEmbeddedObjects() {
         // TODO Auto-generated method stub
         return null;
@@ -539,6 +551,30 @@
 		this.missingCellPolicy = missingCellPolicy;
 	}
 
+    /**
+     * Convenience method to set the active sheet.  The active sheet is is the sheet
+     * which is currently displayed when the workbook is viewed in Excel.
+     * 'Selected' sheet(s) is a distinct concept.
+     */
+    public void setActiveSheet(int index) {
+
+        validateSheetIndex(index);
+        int nSheets = sheets.size();
+        //activeTab (Active Sheet Index) Specifies an unsignedInt that contains the index to the active sheet in this book view.
+        CTBookView[] arrayBook = workbook.getBookViews().getWorkbookViewArray();
+        for (int i = 0; i < arrayBook.length; i++) {
+            workbook.getBookViews().getWorkbookViewArray(i).setActiveTab(index);
+        }
+    }
+
+    private void validateSheetIndex(int index) {
+        int lastSheetIx = sheets.size() - 1;
+        if (index < 0 || index > lastSheetIx) {
+            throw new IllegalArgumentException("Sheet index ("
+                    + index +") is out of range (0.." +    lastSheetIx + ")");
+        }
+    }
+
     public void setBackupFlag(boolean backupValue) {
         // TODO Auto-generated method stub
 
Index: src/ooxml/testcases/org/apache/poi/xssf/usermodel/TestXSSFWorkbook.java
===================================================================
--- src/ooxml/testcases/org/apache/poi/xssf/usermodel/TestXSSFWorkbook.java	(.../https://svn.apache.org/repos/asf/poi/branches/ooxml)	(revision 699004)
+++ src/ooxml/testcases/org/apache/poi/xssf/usermodel/TestXSSFWorkbook.java	(working copy)
@@ -50,6 +50,17 @@
 	    );
 	}
 
+    public void testGetSetActiveSheet(){
+        XSSFWorkbook workbook = new XSSFWorkbook();
+        Sheet sheet1 = workbook.createSheet("sheet1");
+        Sheet sheet2 = workbook.createSheet("sheet2");
+        Sheet sheet3 = workbook.createSheet("sheet3");
+        // set second sheet
+        workbook.setActiveSheet(1);
+        // test if second sheet is set up
+        assertEquals(1, workbook.getActiveSheet());
+    }    
+
 	public void testGetSheetIndex() {
         XSSFWorkbook workbook = new XSSFWorkbook();
         Sheet sheet1 = workbook.createSheet("sheet1");