SetSelectedNotebook

SetSelectedNotebook[notebook]
makes the specified notebook be the currently selected one in the front end.

Setting a particular notebook to be the currently selected one typically makes it the top notebook displayed on the screen.

Making a notebook the currently selected one does not affect the current selection within that notebook, or within other notebooks.

Create two notebook documents:

Make the first one the selected notebook:

Create two notebook documents:

Out[1]=

Make the first one the selected notebook:

Out[2]=

Create a palette for selecting from two existing notebook windows:

SelectedNotebook gives you the notebook object for the selected notebook:

The evaluation notebook can be different from the currently selected notebook: