This thesis examines the concept and practice of partnership in the context of post-16 learning. The study explores the process of partnership working through a qualitative case study of a sub-regional partnership that aims to widen participation in post-16 learning through its collaborative activities. The investigation seeks to learn about the basis of partnership and to identify characteristics that contribute to continued and effective partnership working. Drawing on understandings of partnership in policy, theory and in practice, I develop a more detailed conceptualisation of partnership than is currently available in the field of post-16 learning. The history, development and work of the case study partnership were investigated through a combination of methods including observations of partnership meetings, documentary evidence of partnership working and semi-structured interviews with participants in the case study. The interviews with senior managers of institutions and organisations that provide education, training and guidance for post-16 learners in the Black Country, a sub-region of the Midlands in England, focused on the reasons for participation in a partnership and the aspects of partnership working that contribute to sustainability in partnerships. The findings give a rich insight into the practicalities of working in partnership with individuals and organisations and provide a basis for theorising partnership as a heterogeneous concept and practice rather than a homogenous entity. The case study reveals both the potential of partnership and the challenges to partnership working, such as resource and power differentials. It also shows how social capital can provide the basis for sustained partnership and function as a resource that can be used in similar ways to other forms of capital. This insight is used together with characteristics drawn from the partnership literature to theorise partnership as a continuum of weak to strong forms of partnership, which function on the basis of different types and levels of trust, the operation of formal and informal networks and shared norms and values amongst actors.