Moist convection, the process responsible for torrential rains and lightning, plays a key role in Earth's energy and water cycle and is a major but still uncertain player in model predictions of climate change.  Recent satellite missions and field experiments have begun to constrain the effects of moist convection on clouds and water vapor but present new challenges for understanding and modeling the dynamics of convection and its interaction with aerosols and the large-scale circulation.  Moist convection has been tentatively identified on other planets as well, and its behavior may be central to understanding both superrotating winds on slowly rotating planets such as Titan and the maintenance of jets on the rapidly rotating jovian planets.  Questions raised by recent planetary missions about the role of convection on these planets will be discussed.