Corporate Social Responsibility (CSR) is not a new area for academics or practitioners, but one that has gained momentum in the past three decades. Despite a proliferation of academic research focusing on CSR, much of the literature is either normative in nature, focusing on what organisations 'should do' in terms of CSR, or is centred on identifying the relationship, if any, between CSR and an organisation's financial performance. This has led to a paucity of research exploring the 'how' and 'why' of CSR. Ultimately, whilst the level of academic and practitioner activity in the area is increasing, our knowledge and understanding of CSR in practice is in its embryonic stages. This thesis explores CSR in practice, in-depth. It presents three case studies, based on evidence gathered through semi-structured interviews and focus groups from three UK-based organisations. Each organisation has been recognised as an exemplar of CSR in practice. This research programme presents a number of findings which make a contribution to our knowledge and understanding of CSR. It found that whilst at times being portrayed in the literature as relatively homogeneous, CSR in practice actually consists of a series of disparate, highly heterogeneous activities, which range from being-'business as usual' to peripheral. The research identifies and explores the antecedents to this heterogeneity, including the impact of an organisation's sector, CEO and culture. Furthermore, organisational motives for engaging in CSR play a much greater role in determining its manifestation in practice than previously thought. Contrary to existing studies, this research found the implementation of CSR to be non-linear, and highlights the importance of engaging in both 'implicit' and 'explicit' CSR. CSR in practice is much more convoluted, complex and counter-intuitive than existing research suggests, with academia and practice having developed thinking and arguments on CSR on entirely separate trajectories.