This article describes the core features of outcome research and then explores issues confronting researchers who engage in outcome studies. Using an intervention research perspective, descriptive and explanatory methods are distinguished. Emphasis is placed on the counterfactual causal perspective, designing programs that fit culture and context, and developing nuanced explanations for program outcomes. Five emerging challenges are discussed: (a) adapting interventions to the contexts and cultures in which programs are to be implemented, (b) avoiding potentially false attributions of program failure due to differential implementation, (c) making causal inferences from observational data with propensity score analysis (PSA), (d) examining person-centered outcomes in program evaluation, and (e) adjusting for rater effects in longitudinal research. (Contains 3 figures.)