This chapter discussed a number of methodological considerations that face prevention research. It examined the central importance of theory in design and analysis of prevention studies. It considered the role of factorial invariance in developing culture-specific measures. It discussed the importance of statistical power and how it is dependent on factors other than sample size. It considered growth curve models, survival analysis, and lta, all relatively new procedures for dealing with change over time. It also discussed two approaches to the trait-state distinction and looked at missing data procedures and how important they are for prevention research. Finally, it discussed two general types of models that frequently arise in prevention research, mediation models and models of reciprocal causation, and how the customary ways of testing these models should perhaps be reconsidered.