This thesis is an exploration of the perspectives of recipients and providers of health and criminal justice services about the transitional support needs of arrestees and remand prisoners, leaving short-term custody. The study implements Constructive Grounded Theory Methods, underpinned by the Network Theory of Social Capital as the theoretical framework. Forty-two semi-structured interviews were conducted, with five participant groups; service users (arrestees/remand prisoners), family/carers, mental health staff (criminal justice liaison and mental health in-reach, community mental health teams), criminal justice staff (police/prison officers) and mental health commissioners. Participants provided unique perspectives about the health and social support, available at the transitional points of leaving short-term custody. This was supported by the construction of 11 sociograms for service users, in both arrest (n=5) and remand (n=6) situations, to highlight the availability and functionality of support networks. Transitions are particularly problematic in relation to linking offenders with appropriate community-based mental health services. The over-arching constructed grounded theory is a need for a culture shift within health policy and practice to refocus on transitional care planning to optimise continuous care pathways. Associated themes include 'lack of practical assistance', 'lack of crisis support', 'returning to the security of prison' and 'poor transition planning'. Critical Time Intervention, a variant of case management has demonstrated benefits when applied to mental health and offender populations, transiting from hospital and prison settings. The programme contains all the components of service that service users, carers and staff identified as important to effectively support transitions from short-term custody to the community.