Third-party punishment refers to an individual’s disposition to punish wrongdoers who have not directly harmed them. It appears to be unique to humans and culturally universal. Although this behavioral tendency in adults has been well documented, its ontogeny remains unresolved and controversial. In this review, I present an overview of the developmental literature on third-party intervention or punishment to provide insights into its early ontogeny. First, I review studies that show preschoolers and older children to be agents who punish wrongdoers even when it is costly to do so. I then consider studies of young children as assessors who expect wrongdoers to be punished and positively evaluate those who do so. Next, I present recent studies of preverbal infants to demonstrate two important aspects of third-party punishment: punishment assessors and punitive agents. Finally, I discuss open issues and future directions for understanding third-party punishment in early ontogeny.