Massachusetts Rotary Traffic Rules: Traffic moves in a counterclockwise direction around a rotary. You must always yield the right of way to vehicles already in the rotary (unless directed differently by local signs or police officers) and to pedestrians. You should use your turn signals in the same way as any other intersection: travel through the rotary and, when you are ready to exit, use your right turn signal.
Here's a little shot out to the most well know rotary/roundabout out there:
Paris - Arc de Triumphe