Child maltreatment affects millions of children around the world and is associated with serious short- and long-term consequences, such as depression, substance abuse, post-traumatic stress symptoms, and aggression. Unfortunately, programs aimed at reducing child maltreatment show only small to moderate overall effects. An explanation for these results may be that interventions provided by youth and family services are insufficiently personalized to the individual risks, needs, and characteristics of families at risk. The overarching aim of this dissertation was to increase the knowledge on treatment tailoring in youth and family services, based on the three core principles of the Risk Need Responsivity model. The following studies were performed to achieve this aim: a meta-analysis on the effects of adhering to the Risk, Need, and Responsivity principles in family interventions aimed at reducing criminal recidivism of delinquent youth (Chapter 2), a qualitative study on the clinical value and usability of a needs assessment tool (ARIJ-Needs) in the decision-making processes of practitioners choosing an appropriate intervention for families that are involved in child protection services (Chapter 3), a qualitative study on the clinical value of applying the responsivity principle in child protection services (Chapter 4), a study on gender differences in criminogenic risk factors between male and female domestic violent perpetrators (Chapter 5), and a study on the distinctiveness of two maltreatment dimensions, i.e., abuse versus neglect, and emotional versus physical maltreatment, in identifying developmental problems in a clinical sample of victims of child maltreatment (Chapter 6).