Investments in youth are particularlyimportant in light of the unprecedented numbers of youngpeople now entering their reproductive and early adultproductive years. Of the more than one billion youth aged15-24, 86 percent live in developing countries. This guideis for those involved in appraising the economic merits ofyouth projects or projects with an important youthcomponent. It builds on two previous publications in the HNPDiscussion Paper series, Assessing the Economic Returns toInvesting in Youth in Developing Countries (Knowles andBehrman 2003), and The Economic Returns to Investing inYouth in Developing Countries: A Review of the Literature(Knowles and Behrman 2005). The guide is designed to explainand illustrate basic economic principles relevant to ex anteproject appraisal, and their application to the task ofmaking choices related to youth projects. It is alsointended to familiarize those who do not specialize in youthprojects, with some of the issues particular to youthprojects, and to provide some basic understanding of theconcepts, relationships and data relevant to undertakingeconomic analysis of youth projects. The guide comprisesseven sections. Following a brief introductory Section 1,Section 2 sketches a framework for economic analysis ofyouth projects, and the basic economic motives for policiesand policy options. Section 3 turns to estimating costs,effectiveness and benefits. Section 4 considers poverty andgender analysis. Section 5 includes seven illustrative casestudies covering a variety of youth investments in severaldifferent countries. Section 6 presents model terms ofreference for the economic analysis of a hypotheticalcontinuing education project in Serbia-Montenegro,corresponding to one of the case studies presented inSection 5. Section 7 provides a list of references.