Most Cochrane Reviews compare the effects of different interventions or strategies on outcomes. But, we are now seeing reviews that use qualitative research evidence to explore why things happen, more than what things happen. Claire Glenton from the Norwegian Knowledge Centre for the Health Services in Oslo describes one of the early examples of this type of review. The review was written by a team from Norway, South Africa, the UK and Iran and was published in October 2013 and looks at the role of lay health workers in maternal and child health.