Publisher Summary This chapter discusses various studies in which calorimetry have been used to characterize zeolites, oxides, and metallic catalysts. It is apparent from the results in the literature that microcalorimetry is a very powerful technique even if it does not provide direct information about the molecular nature of the adsorbed species. The chapter describes the way the adsorption enthalpy profile of a probe molecule can be used to characterize the surface sites. Adsorption microcalorimetry permits an accurate determination of the strength and strength distribution of surface sites based on the heat of adsorption of suitable probe molecules and the differential heat versus coverage curve. A survey of applications of microcalorimetry for heterogeneous catalysis are described in the chapter with particular emphasis on the determination of the acid–base properties of zeolites, molecular sieves, metal oxides, and supported metal oxides. Additional applications of the study of reducible metal oxides and their redox character are discussed in the chapter.