The concentrations and the cycling of water vapor in the atmosphere will change as the climate warms, resulting in changes in the mean distribution of precipitation as well as in extreme precipitation events. This talk will be an introduction to the physics controlling different aspects of this problem. including the response of the global mean precipitation, controlled by the energy balance of the troposphere; the response of the horizontal vapor transport, controlled by the increasing moisture content of the atmosphere and resulting in the "wet-get wetter" and "dry-get drier" paradigm in the absence of changes in atmospheric circulation; and how the changes in atmospheric circulation, such as the poleward shift of the midlatitude storm tracks can be understood as responses to the changes in water vapor transport. Key observations supporting these theories will be highlighted.