This chapter reviews knowledge about the most important family influences on offending and about the most effective family-based intervention programmes to reduce offending. Prospective longitudinal studies yield the most convincing information about family influences on offending, while randomized experiments yield the most convincing information about the effectiveness of interventions.A great deal is known about risk factors for offending, but less is known about protective factors. The most important family risk factors include poor child-rearing (poor supervision, harsh or erratic discipline, parental coldness, low parental involvement), teenage parents, child physical abuse or neglect, parental conflict, disrupted families (caused by parental disharmony), criminal parents and large family size. In risk-focussed prevention, intervention techniques target key risk factors such as poor child-rearing. Home visiting programmes including general parent education, and parent management training that teaches parents child-rearing skills, are both effective in reducing later offending. Named programmes such as The Incredible Years, Triple-P, Functional Family Therapy, Treatment Foster Care and Multisystemic Therapy, are effective. The financial benefits of these programmes exceed their financial costs. A national prevention agency is needed in all countries to fund and coordinate the delivery of effective prevention programmes.