This chapter reviews studies on public-private crime prevention partnerships in public spaces. The focus of the chapter is on successful case studies, while also addressing ethical issues and practical obstacles. The first section provides brief accounts of the development of policies regarding partnerships in security, including a variety of examples in practice, outlining how the work of the security industry fits within a successful situational and problem-oriented crime prevention framework. The chapter then considers the potential role of private security in foot patrols supporting police and in Business Improvement District programs. The focus then shifts to six evaluated case studies, addressing development processes, interventions, and impact measures. The final section reviews the likely ingredients for success, with the provision of a set of guidelines for ensuring accountability and optimal outcomes in police-security collaboration, including through optimal regulation of the security industry.