This research explores the learning of volunteers who are being trained to perform service-providing roles within UK health and social care charities. Within these charities, volunteers often perform complex roles in dynamic environments, supporting service users and addressing challenging causes. This thesis argues that the charity and voluntary environment offers certain affordances, and also constraints, that provide opportunities for transformative learning experiences. The limited previous studies on the learning of volunteers have tended to concentrate on training evaluations or informal learning 'on the job', resulting in an unhelpful formal/informal dichotomised approach to learning. The research proposes that this approach has been unable to offer a detailed insight into the learning experienced by volunteers within the training process. In particular, this dichotomised view has been unable to account for both the learning of scientific concepts, such as the specific health conditions these charities are addressing, and everyday experiences of both volunteers and service users that are integral to the learning process.To address this gap, the thesis draws upon Cultural-Historical Activity Theory (CHAT), which is an approach grounded in Hegelian dialectics. Specifically, the CHAT-informed theories of expansive learning (Engeström, 1987) and Transformative Activist Stance (TAS) (Stetsenko, 2008) are synthesised to examine how volunteers interact with and within the charity environment through practices of training. Through this perspective, learning is conceptualised as a form of individual and social transformation, which expands the possibilities for collective activity. Expansive learning and TAS have previously been drawn upon to provide insight into learning in the workplace and in projects of social change respectively. However, so far the theories have not been focused on learning within the charity and voluntary environment.A multiple case study of three health and social care charities based in North West England provides the empirical data for the research. Each charity addresses a complex health and social cause, including stroke, sexual violence and HIV, and relies on volunteers to help provide services. Multiple qualitative methods, including observations of training, charity staff interviews, along with interviews and focus groups with volunteers, allow a range of perspectives and positions to be taken into account in line with the epistemology of the study. Data are analysed through the process of abduction drawing upon a CHAT-informed theoretical framework.The thesis intends to contribute to knowledge in two main areas. Firstly, it aims to increase understanding of learning within volunteer training, including how learning in the charity environment can be supported, sustained and made meaningful to enable transformative experiences. Secondly, it aims to theoretically advance CHAT, and the charity and voluntary environment is presented as a fruitful setting for developing particular aspects of the theory, such as emotion and agency.