Three types of explanation in evaluation are discussed: causal explanations, explanations of actions, and explanations of value judgments. The role and importance of each form is addressed, as are alternate approaches to providing such explanation. The concept of explanation is defined as anything said or done to help someone understand something. The classification of explanation is based on a distinction between types and methods. Methods are identified and defined: descriptive, narrative, genetic, experimental, and theoretical. Two of these types of explanation--action and value explanation--have generally been neglected in evaluation. Causal explanation has been interpreted in a narrow fashion, and causal claims not satisfying its requirements have been regarded as unsound. Action and value explanations have objective significance which is capable of being spelled out empirically, and they are therefore susceptible to public testing. It is concluded that, in spite of imperfect circumstances, there are ways of responsibly arriving at intellectually and morally sound explanations; although the available means are demanding on the judgment and conscience of the evaluator. (Author/GK)