Maternal mortality reduction in many countries is unlikely despite the availability of inexpensive, efficacious interventions that are part of official policy. This article explores the reasons why, based on research on maternity services in Bangladesh, Russia, South Africa and Uganda. A simple dynamic responses model shows that the key to understanding challenges in implementation lies in the reflexive, complex and dynamic responses of health workers and community members to policies and programmes. These responses are "dynamic" in that they arise due to forces from within and outside the system, and in turn exert forces of their own. They result in the difference between the health system that is envisaged in policy, and what is implemented by health workers and experienced by users. Programmes aiming to improve maternal health are not only technical but also social interventions that need to be evaluated as such, using methodologies that have been developed for evaluating complex social interventions whose aim is to bring about change. The components of effective programmes have been defined globally. However, in getting what works to happen, context matters. Thus, technical advisors need to give "advice" more circumspectly, local programme managers must be capacitated to make programme-improving adjustments continuously, and the detail related to process, not just outcomes, must be documented in evaluations.