Organisations with explicit social missions such as social enterprises, impact investors, nonprofits, and foundations are under increasing pressure to illustrate the impact of their activities on the social problems they claim to be addressing. These trends have resulted in an increasing sophistication of attempts to measure, assess, and report social impact across sectors. However, research in the field of social entrepreneurship has not sufficiently addressed the complex nature of impact assessment, nor how it is enacted in everyday organisational activities. This chapter aims to explain how practitioners cope with the complexity of impact assessment in their everyday activities. Drawing on practice theory, this chapter argues that impact assessment should be grounded in everyday experience and practice. This chapter builds on the emerging evidence of, and develops a research agenda for, the ‘practice turn’ in impact assessment in social entrepreneurship.