This chapter highlights how the evolving field of implementation research is being used to address problems of implementation of health policies, programs, practices, and technologies in low and middle-income countries (L&MICs). Implementation research offers a way to understand and address implementation challenges and contribute to building stronger health systems within the realities of specific and changing contexts. It is used to assess how and why interventions work, including the feasibility, adoption, and acceptance of interventions and their coverage, quality, equity, efficiency, scale, and sustainability. A well-designed research question is critical to successful implementation research, and provides the basis for choosing the research methods and how likely the research will influence policy and practice. In describing the theories, frameworks and tools used in implementation research, they are shown to be well suited to address inter-dependent and complex problems around improving people’s wellbeing – a critical mandate for achieving Universal Health Coverage and the Sustainable Development Goals.

Decisions taken by stakeholders at all levels of health systems can benefit from the use of different types of evidence drawn from heterogeneous research fields – including epidemiology, clinical and basic biomedical research, and health policy and systems research (HPSR). However, out of these diverse forms of evidence, HPSR is relatively underused and under-funded. Challenges associated with the use of HPSR in health systems in low- and middle-income countries (L&MIC) include the lack of opportunity and resources, the need for greater capacity for the generation and use of evidence, and fundamental problems around how the research agenda is framed. Evidence informed decision-making in L&MICs can be improved by better alignment of HPSR with health system needs, institutionalizing the use of HPSR evidence, and strengthening individual capacities to generate and use HPSR evidence. Several global, national and local-level initiatives have helped take strides in these areas, but more work and investments are needed to strengthen the use of appropriate evidence, especially HPSR evidence, in health systems.