Where can I find the Decimate modifier? I need to decimate a 3d-scanned image.  I am in Object Mode, but I do not see the Modifiers Panel.  The wiki says that F9 will display the Modifiers panel, but this does nothing in my Blender session.  I am running Blender 2.70 on Windows 7.
Thank you for your time.
You must have an object selected for the modifiers panel to be visible.

Once you have an object selected (yellow outline), it will be in Properties > Modifiers. Then click on Add modifier and select Decimate: