Advisory committees are used often in evaluation studies, yet this practice is little discussed or reported. This issue is the first full-length text devoted to the purpose, practice, and scholarship about this type of formal, structured advice. It includes case studies and analyses of these to answer such basic topics as: What is an evaluation advisory group (EAG)? Why (not) use an EAG? How to organize an EAG, and how to evaluate it? The reader will learn how to view the EAG as a structure of expertise, its use for political legitimacy, and as a response to a variety of constituencies. Guidelines on how to recruit, select, orient, train, monitor, assess, and evaluate EAG members are also included. This is the 136th volume of the Jossey-Bass quarterly report series New Directions for Evaluation, an official publication of the American Evaluation Association.