This chapter describes a concrete process that stakeholders can use to make predictions about the future performance of programs in local contexts. Within the field of evaluation, the discussion of validity as it relates to outcome evaluation seems to be focused largely on questions of internal validity (Did it work?) with less emphasis on external validity (Will it work?). However, recent debates about the credibility of evaluation evidence have called attention to how evaluations can inform predictions about future performance. Using this as a starting point, we expand upon the traditional framework regarding external validity that is closely associated with Donald Campbell. The result is a process for making predictions and taking action that is collaborative, systematic, feasible, and transparent.