Although lagging behind green finance, the market for social financial instruments, such as social bonds or social equity funds, has gained traction in recent years. This chapter focuses on the conceptual underpinnings of social finance. It also provides an overview of the heterogeneous definitions of social investments common in financial markets. It distinguishes between a focus on the impact of goods and services produced and one on process-related impacts in social investment criteria. The chapter describes a positive selection of sectors, exclusion of specific sectors, best-in-class procedures, and applying minimum standards as selection procedures commonly used for social financial instruments. The diversity of existing criteria and selection procedures in financial markets increases transaction costs, can facilitate deceptive practices, and might lead to adverse selection. Public governance frameworks are thus necessary to set common standards for social financial instruments.