The environmental effects of development are mitigated from two distinct perspectives – ex ante, through environmental and social impact assessment (ESIA), and ex post, through environmental management systems (EMS). Whilst recognising the range of variations that exists, this chapter focuses on the key principles associated with the development and implementation of project level environmental and social management plans (ESMPs). It explains the generic outline methodology for developing an ESMP and provides guidance on the likely structure and content. The key to advancement of ESMP practice is to enhance learning from experience at all levels of application and practice. A number of different organisations have produced good-practice guidance which addresses ESMPs and a selection is now briefly outlined. The 1990s witnessed the evolution of practice-led initiatives to integrate environmental assessment and management. Whilst most multilateral development banks now have policy requirements and guidance on ESIA, the World Bank first developed its environmental guidelines in 1988.