This lecture delves into the complex world of receptor-ligand interactions, exploring topics such as binding, dissociation, and equilibrium constants. It covers the quantitative aspects of these interactions, including stoichiometry, thermodynamics, and kinetics. The lecture also discusses the methods used to determine binding, the localization of receptors in tissues, and the quantification of receptor-ligand interactions in various assay formats. Through the analysis of energy scales and residence times, the instructor provides insights into the strength and duration of these interactions, crucial for understanding medical chemistry applications.