The UK government’s IAPT programme has introduced new roles, therapeutic practices and interventions, within primary care mental health. An expanding workforce of Psychological Well-being Practitioners (PWP) and high intensity Cognitive Behavioural Therapists (HIT) has been recruited and trained since 2008, amidst controversy over policy aims, implementation and service delivery models. For this new workforce to be effective and sustainable, the psychosocial and organisational dynamics that surround the work and training system need to be better understood. Strong staff and public expectations, competing ideologies and professional claims all affect how practitioners deliver patient care. Similarly, a complex ecology of practices exists in each local setting, which makes demands of practitioners’ organisational, interpersonal and clinical skills and resilience. This study explores how practitioners manage the transition into role during and after training, the dilemmas they face in practice, and their changing identifications over time. It takes a longitudinal and holistic perspective on both PWP and HIT journeys through the IAPT system, drawing on psychoanalytically-informed classroom-based observations, practitioner narratives and staff interviews and using a range of in-depth analytic methods. By focusing on contributions from governmentality theory, sociology of the professions, theories of practice, psychosocial studies and applied psychoanalysis, the thesis shows connections and tensions between the discourse of evidence-based policy, New Public Management and practitioner experience. This contrasts with the atheoretical and instrumental tendency seen in Health Services’ Research. It shows unequivocally that the professional status of IAPT roles, is insecure. PWPs and HITs have an organisational, rather than occupational identity and share characteristics with historical semi-professions, in their strong collective beliefs and sense of having ‘legitimate aspirations denied.’ IAPT’s distinctive culture of practice and the feelings evoked by high volume, low intensity work, have consequences for individuals’ commitment and ability to stay in role, and for the services’ future sustainability.