Despite much enthusiasm for the practice of peer mentoring by ex-offenders it has received very little empirical scrutiny. This thesis examines the micro dynamics and intimate interactions within these relationships. In doing so it highlights how mentors are often much more than functional additions to existing criminal justice systems. They are also presented as teachers, co-operators and critical agents. The narratives in this study highlight how dominant forms of knowledge often minimise or miss the lived experiences of crime and change. In contrast, peer mentors place lived experiences at the centre of their approach and in doing so they critically question exclusionary practices and re-humanise themselves and their peers. The work of peer mentors also highlights and at times challenges the hidden power dynamics that are subsumed when ‘regular’ interventions take place. But, mentoring cannot avoid or operate outside of these power relationships. It can and does generate other power dynamics. Whilst many of these complex relations remain hidden in current evaluations of the practice they are rendered visible here. Data were obtained from qualitative interviews with eighteen peer mentors, twenty peer mentees, four service coordinators and two Probation officers, who were drawn from a range of voluntary sector providers in the North of England. Observations of practice were also carried out, including: volunteer recruitment processes; training courses; and formal supervision sessions. Where possible mentors were also observed facilitating group work with their peers. The analysis of the data drew upon techniques of thematic analysis and critical discourse analysis focusing upon how mentoring was described, performed and justified by participants. As a result of this analysis five overarching themes emerged. These are: identity, agency, values, change and power