This is the first guidance note in a four-part series of notes produced by InterAction to support management, program <span class="attribute-to-highlight medbox">and</span> M&E staff in international NGOs to plan, design, manage, conduct <span class="attribute-to-highlight medbox">and</span> use impact evaluations. This first guidance note, Introduction to Impact Evaluation, provides an overview of impact evaluation, explaining how impact evaluation differs from – <span class="attribute-to-highlight medbox">and</span> complements – other types of evaluation, why impact evaluation should be done, when <span class="attribute-to-highlight medbox">and</span> by whom. It describes different methods, approaches <span class="attribute-to-highlight medbox">and</span> designs that can be used for the different aspects of impact evaluation. The guidance note is also available in French, Arabic <span class="attribute-to-highlight medbox">and</span> Spanish on https://www.interaction.org/impact-evaluation-notes.