This book considers the process of impact assessment and shows how and why it needs to be integrated into all stages of development programs - from planning to evaluation. Its basic premise is that impact assessment should not refer to the immediate outputs of a project or program, but to any lasting or significant changes that it brought about. From a theoretical overview, the book moves on to discuss the design of impact-assessment processes and a range of tools and methods, before illustrating its use in development, in emergencies, and in advocacy work. It ends by exploring ways in which different organizations have attempted to instititutionalize impact-assessment processes and the challenges they have faced in doing so. In-depth case studies by partner organizations of Oxfam and Novib as well as by some Oxfam staff show how a variety of approaches to impact assessment - qualitative, quantitative, and participatory - in a range of situations from large-scale integrated development programs to projects involving only one community. These include impact studies undertaken by BRAC and PROSHIKA in Bangladesh, the evaluation of a post-conflict rehabilitation program in El Salvador, a long-term study of the effectiveness of environmental projects in Zimbabwe, and a retrospective review of a neighborhood project in the UK.