How to make Pop Up! shows once per session?

Hello, how can I setup Pop Up! so that it shows to the visitor only once per visit?

So that when he comes to my site on any page, the popup shows. But as he navigates the site, the popup won't show again. He then closes the browser, and next time he comes to my site again, the popup shows again once.

I can't find the Conditions to do it.

Thanks,
Jimmy