This Review addresses a mismatch between what is known about how to respond to particular health problems in poor economies and what is actually done about them. It focuses on one cause of the problems that ensue from the mismatch – capacity constraints. Weak capacity at a number of levels in the institutions and interfaces between knowledge generation and use in policy-making has been identifi ed by the Alliance for Health Policy and Systems Research (HPSR) as a key strategic issue in addressing health care in low-income countries. Capacity is a widely but often superfi cially used term. This Review explores capacity issues underlying different aspects of the relationship between two key groups – policy-makers and researchers – using a new conceptual framework (see Figure 1). Accordingly, the analysis focuses on capacity constraints in research priority-setting; generation and dissemination of knowledge; fi ltering and amplifi cation of evidence; and policy processes. The framework could be applied to analyse critical areas for capacity development in-country.