Social impact assessment (SIA) is the process of identifying and managing the social impacts of industrial projects. It can also be applied to policies, plans and programmes. SIA is used to predict and mitigate negative impacts and identify opportunities to enhance benefits for local communities and broader society. Central to the principles and practice of SIA is the involvement of affected communities and other stakeholders in the process. SIA should inform decision-making by government and companies from the early stages of a project. Equally important is the role of SIA in the ongoing management of social issues throughout the whole project cycle until decommissioning and closure. As such, the social management plan that derives from an SIA is extremely important. SIA is also an essential foundation for community agreements and in processes of free, prior and informed consent (FPIC) conducted with indigenous communities before the start of industrial development projects. This briefing explores the core principles of SIA and the SIA requirements of selected international instruments. It also considers some of the key challenges to implementing SIA in practice and offers some recommendations for future practice.