I need to use conditional formatting to highlight certain cells. Example:

Column A ........................Column B
1 Due Date .....................Completion date
2 Due Date ......................Blank

I need to highlight A2 if B2 is blank.

I can format it to highlight Column A cells that fall within a date range, but I haven't come up with a formula that will highlight cells in Column A if the corresponding cell in Column B is empty. Any help would be appreciated.