This issue of New Directions for Evaluation looks back at the past twenty years of the American Evaluation Association, from its inception to current research, highlighting important moments and enduring issues in the discipline and profession of evaluation. The issue includes a very brief history of NDE--including the journal's purpose, the various foci, how the journal has operated, and such events as the change in the journal's name. The issue also looks at the substance of NDE over the past twenty years, including an analysis of the coverage of cultural diversity issues. But much of the issue is devoted to "greatest hits" chapters that have appeared in prior NDE issues, each of which is introduced by an analysis of what makes it a significant contribution to the evaluation literature. The American Evaluation Association (AEA) celebrated its twentieth birthday in 2006. The partnership between AEA and New Directions for Evaluation has spanned this time and indeed stretches back further to AEA's precursor associations, the Evaluation Research Society and ENet. This is the 114th volume of the quarterly report series New Directions for Evaluation , a publication of Jossey-Bass and the American Evaluation Association.