Publisher Summary If distributions of temperature and moisture violate the conditions for hydrostatic stability, small vertical displacements produce buoyancy forces that accelerate parcels away from their undisturbed positions. Unlike the response under stable stratification, this reaction leads to finite displacements of air. Fully developed convection then drives the stratification toward neutral stability by rearranging air. Two classes of instability are possible: parcel instability and wave instability. Parcel instability follows from reinforcement of air displacements by a negative restoring force, such as that occurring in the development of convection. Wave instability occurs in the presence of a positive restoring force, but one that amplifies parcel oscillations inside wave motions. Unstable waves amplify by extracting energy from the mean circulation. The simplest form of large-scale instability relates to the inertial oscillations. More relevant to the large-scale circulation is instability associated directly with shear. Shear instability is of the wave type, so it requires a more involved analysis than that applying to an individual parcel.