This chapter presents an overview of calorimetry and its role in radiation dosimetry, starting with the fundamental theory of measuring minute temperature rises in an absorbing medium. Building on this foundation, water and graphite calorimetry are explored in detail, including key corrections and technical considerations needed for accurate dose measurements. The discussion also addresses various clinical beam modalities—such as photon, electron, proton, carbon-ion, and brachytherapy sources—demonstrating the practical application of calorimetric techniques in diverse treatment settings. By combining core principles with real-world considerations, this chapter highlights the continued relevance of calorimetry in delivering precise and reliable dosimetry.