Can I use SmarTrip on Metro buses?

Stupid question, I know, but to be honest I've never actually taken a bus. If the answer is yes, are all buses equipped to handle SmarTrip or only certain ones? And while we're at it, how do bus/metro transfers work? Do I need to get one if I'm using a SmarTrip card?

All Metrobuses and most suburban bus lines take SmarTrip. In fact, if you use your SmarTrip, it costs less than if you pay cash. No need to worry about a transfer--it's automatic. So if you exit a Metro station with your SmarTrip and then hop a Metrobus, just swipe the same card, and it will charge only 35 cents. Transfer between buses, swipe the card, and it will not charge at all.

In fact, I'm pretty sure that when SmarTrip was introduced, all Metrobuses got it pretty quickly. It took a while for the suburban lines to get it, but it's a lot easier now.

You can also add money to your SmarTrip on buses, but it's a pain in the butt, and you'd be better off doing it in a Metro station.

Sadly, they have not instituted a discount for transfering from bus to rail, although you'd think they could.