Social Enterprises (SEs) are normally micro and small businesses that trade to tackle social problems, and to improve communities, people’s life chances, and the environment. Thus, their importance to society and economies is increasing. However, there is still a need for more understanding of how these organisations operate, perform, innovate and scale-up. Obtaining this understanding is the main driver of this paper, which explores the SE activities to manage their knowledge. Interviews from 21 owners and senior members of SEs in UK confirmed that SEs possessed valuable tacit and explicit knowledge about their organisation, practices, experiences and work with communities and costumers. This knowledge is managed informally and, when acquired, is not always converted into usable knowledge, applied to create value, and protected from inappropriate or illegal use. Thus, SEs need to know what they know and manage effectively that knowledge. This can help them to acquire, convert, apply and protect all their knowledge that would result in added value to their organisation and stakeholders, legitimised their practice, adjusted and defined their operational and strategic direction, and informed the measurement of their social impact. This paper contributes to SE and Knowledge Management researchers, SE practitioners and organisations supporting SEs.