High temperature oxide melt solution calorimetry is a versatile technique for studying the energetics of formation, solid solution mixing, phase transition, and order/disorder in complex perovskites. The methodology is described and examples of both present and possible future applications given. The stability of the perovskite structure diminishes as the tolerance factor deviates from unity and increases as the size (and basicity) of the A-site cation increases. High pressure lithium niobate and perovskite structures are formed for a number of silicates, gerrnanates, and titanates. Their energetics become less favorable as the A-site cation radius decreases. Ordered double perovskites are favored at high pressure. Such materials as well as the vacancy-ordered brownmillerite structures are only marginally energetically stable with respect to end-member perovskites. Thermocheniical data suggest that "disordered" perovskite phases in fact contain pervasive clustering and/or short range order.