Has the Properties window gone missing in Revit? or any other window for that matter. Well here are the two main reasons this has happened and how to get it back.
1 Merged Windows
You can merge two windows together in Revit to save on screen space. You do this by dragging one window over the top of the other window. When you do this both windows exist in the same space, you can switch between the two windows by clicking on the tab at the bottom for the window you wish to be displayed.
When this happens accidently though it can be difficult to separate them again, bit a simple trick is to grab the window by its tab at the bottom and then drag it out to separate them with the left mouse button.
2 Closed Window
At some point you are going to accidently close the property window, this could be done by clicking the little x in the top right corner or by clicking one of the properties buttons that exist in various places in Revit.
One this happens you will need to reopen it again, this can be done easily via the View tab on the Ribbon bar. Simply go to User Interface on the left and from the drop down it gives you tick Properties to turn the Properties window back on.