Concern for evaluation theoretical prescriptions emerged about 40 years ago, giving it a history that is both recent enough to be part of the living experience of many of today's theorists and old enough to afford an opportunity for an analysis of how the field has evolved over time. This book examines current evaluation theories and traces their evolution with the point of view that theories build upon theories and, therefore, evaluation theories are related to each other. Initially, all evaluation was derived from social science research methodology and accountability concerns. The way in which these evaluation `roots' grew to form a tree helps to provide a better understanding of evaluation theory. Thus, the book uses an evaluation theory tree as its central metaphor. The authors posit that evaluation theories can be classified by the extent to which they focus on methods, uses, or valuing; these three approaches form the major limbs of the tree. In addition to the authors' overview, which analyzes the evaluation theory tree and connections among theories, the book contains essays by most of the leading evaluation theorists. In these pieces, the evaluators comment on their own development and give their views of their placement upon the tree.