Because there are many users that have wide screens or ones with a high resolution, sometimes it is more efficient to work with multiple Microsoft Excel worksheets that are opened at once. By default, every time you open a new spreadsheet Excel creates a new window for each one. In this case, you must switch between windows in order to work with them (and this can be frustrating if you need data from all or part of them):

• use the View -> Window -> Switch Windows list;
• use Ctrl+Tab or Ctrl+F6 to move to the next spreadsheet;
• use Ctrl+Shift+Tab or Ctrl+Shift+F6 to move to the previous spreadsheet;

If you want to open multiple spreadsheets at once in MS Excel 2007 and 2010 you can use View -> Window -> Arrange All

MS Excel 2007 and 2010 View - Window Menu

and select the layout for your spreadsheets.

Arrange Windows in Excel 2007 and 2010