Advantage is a spot treatment you put on the napes of their necks, and it kills all the fleas on them and in the places where they sleep.

Frontline is similar, but I tried this the last time, and wasn't happy with it. It didn't kill as many fleas, and didn't last as long. I'm going back to advantage next chance I get.

It lasts 30 days, and I adore it. No pills, nothing internal, and it works like a charm. You'll find dead fleas in their sleeping places the next day.