Partnerships between businesses and nonprofit organisations are an increasingly prominent element of corporate social responsibility implementation. The paper is based on two in-depth partnership case studies (Earthwatch–Rio Tinto and Prince’s Trust–Royal Bank of Scotland) that move beyond a simple stage model to reveal the deeper-level micro-processes in the selection, design and institutionalisation of business–NGO partnerships. The suggested practice-tested model is followed by a discussion that highlights management issues within partnership implementation and a practical Partnership Test to assist managers in testing both the accountability and level of institutionalisation of the relationship to address any possible skill gaps. Understanding how CSR partnerships are implemented in practice contributes to the broader CSR and partnership literatures a context-specific level of detail in a systematic way that allows for transferable learning in both theory and practice.