Successive UK governments have sought to promote the role of the voluntary sector in criminal justice, a field traditionally dominated by public sector provision. A new wave of reform launched by the Conservative-led Coalition government sought to outsource probation services and introduce a 'payment by results' model to reward success in reducing reoffending rates. A new market for rehabilitation services has thus been under construction, based on 'prime' contractors and supply chains of sub-contracted providers. How would voluntary sector organisations fare in such a market? This chapter provides a review of these developments, offering an in-depth examination of the voluntary sector's position in an unsettled criminal justice field at a crucial early stage of market shaping. The chapter assesses the attempts by voluntary sector advocates, and voluntary sector organisations themselves, to establish and maintain a viable footing in the emerging landscape of criminal justice.