"This first guidance note, Introduction to Impact Evaluation, provides an overview of impact evaluation, explaining how impact evaluation differs from – and complements – other types of evaluation, why impact evaluation should be done, when and by whom. It describes different methods, approaches and designs that can be used for the different aspects of impact evaluation: clarifying values for the evaluation, developing a theory of how the intervention is understood to work, measuring or describing impacts and other important variables, explaining why impacts have occurred, synthesizing results, and reporting and supporting use. The note discusses what is considered good impact evaluation – evaluation that achieves a balance between the competing imperatives of being useful, rigorous, ethical and practical – and how to achieve this. Footnotes throughout the document contain references for further reading in specific areas." (Introduction, p.1)