This policy brief draws on research, which sets out to understand how practitioners design interventions within programmes using a market systems approach. This key step in moving from inception to implementation has often proved difficult. Programmes have suffered from ‘paralysis by analysis’ or have rushed into interventions that have not delivered the desired results. The research was mainly informed by extensive interviews with practitioners and the results reflect their experience and views. Practitioners focused mostly on the processes of design that they had followed and factors that affect these processes. These processes varied widely, much more widely than our hypotheses assumed.