This book delivers a detailed overview of the essentials of cold and ultracold chemistry for advanced graduate students. Beginning with descriptions of cold and ultracold temperatures in chemistry, the chapters of the book then take the students through the fundamentals of scattering theory, light-matter interaction, reaction dynamics and interactions of cold molecules and atoms. The author focusses on the fruitfulness of the topic while inspiring readers to comprehend the basics of these fascinating reactions and their underlying interactions. This book essentially includes the material which was formerly available in special review articles. This book offers readers, working in the arenas of ultracold gases, physical chemistry and chemical physics, the tools they require to submerge themselves in the world of cold and ultracold chemistry. This book unlocks the exhilarating chemical laws governing chemistry at a low temperature.