The private sector has become an important partner in development interventions that aim to make market systems more favourable for smallholders and low-income consumers of food. How to evaluate these inclusive business programmes is the central theme of this IDS Bulletin. It presents real-world experiences of practitioners and academics using theory-based evaluation. This introductory article highlights the approaches and methods used to assess systemic change and provide learning for adaptive management. It acknowledges the limits to attributing outcomes to programmes alone and proposes a way to generalise about effectiveness where outcomes are highly contingent on a specific contextual embedding. The article explores the synergy of the iterative reflections on the theory of change, the analytical approach of realist evaluation, and the conceptualisation of changes in firms’ practices as emerging from behaviour systems where the motivations, opportunities, and capabilities of firms are not equally distributed.