Sound evaluation planning requires numerous decisions about how constructs in a program theory will be translated into measures and instruments that produce evaluation data. This article, the first in a dialogue exchange, examines how decisions about measurement are (and should be) made, especially in the context of small-scale local program settings. Rigorous measurement strategies will increase the credibility of a study's conclusions, but they usually entail various kinds of costs. In making measurement decisions, evaluators must establish standards for strength of evidence that a given measure produces, weigh alternative measurement options, and communicate carefully with clients and other stakeholders about the measurement requirements in a given evaluation. (Contains 2 figures and 1 note.)