Metalorganic functionalization is a process in which a surface is covered by a metalorganic molecule, that is, a molecule with a metal center and organic ligands. Many current and future areas of technology depend on metalorganic functionalization to build nanometric and molecular devices with defined electronic, chemical, and interfacial properties. Due to the molecular-level precision required, surfaces functionalized with metalorganic compounds are often synthesized, evaluated, and characterized in vacuum conditions. This article provides an overview of key concepts, methodologies, and examples of metalorganic functionalization. Applications are reviewed depending on whether the metalorganic-surface construct is the desired product (as is the case for molecular electronics, sensing, and heterogeneous catalysis) or if it is the first of a series of steps towards the formation of a new material (as is the case in thin film growth for microelectronics and photovoltaics). A brief perspective on the opportunities and challenges for metalorganic functionalization is provided.