The electrical, magnetic, optical, and transport properties of perovskites are controlled by their structure, which is in turn a consequence of atomic scale interactions that are reflected in their thermodynamic properties. High temperature oxide melt solution calorimetry is a versatile tool for determining such energetics. After an overview of the general thermodynamic factors determining perovskite stability, this contribution concentrates on the thermodynamics of three important systems. The first is BaTiO 3-SrTiO3-CaTiO3, where new enthalpy data help separate the effects of cation size and lattice distortion. The second is strontium-doped lanthanum ferrite-manganite (LSFO-LSMO), where defect chemistry, transition metal oxidation state, and magnetism all play important roles. The third is lead magnesium niobate - lead titanate (PMNPT), where short range order, symmetry changes, and competition of other phases (e.g. pyrochlore) are important considerations.