Chapter 3 presents the design and the methodological framework of this quasi-experimental prospective longitudinal study, including the sampling procedure. It centers on social-therapeutic facilities within the German prison system, the rationale and strategies of which form the primary context. A description of the design is followed by an in-depth overview of the factors analyzed concerning recidivism among persons convicted of sex offenses as well as violent offenses. Overall, the study examines the influence of (a) criminogenic, offender-related factors; (b) therapeutic measures; and (c) offense-specific factors, including the post-release situation. The chapter then outlines the sample recruitment and data collection procedures and sets the stage for a comparative analysis between the participant sample and a non-participant sample drawn from the inmate population of the relevant prisons. It concludes with a descriptive overview of the study participants’ core characteristics, such as age, offense types, and treatment status.