Randomized controlled trials (RCTs) are important for evaluating interventions, and qualitative research is increasingly recognized as being crucial to the success of this enterprise. We aimed to describe and demonstrate a temporal parallel purpose framework to help researchers understand how to make optimum use of qualitative research before, during and after RCTs. This framework sets out specific rationales for conducting qualitative research at each stage of a trial, where the rationales presented relate to both the intervention and evaluation methodology.. To read the full article, log in using your NHS Athens details. To access full-text: click “Log in/Register” (top right hand side). Click ‘Institutional Login’ then select 'OpenAthens Federation', then ‘NHS England’. Enter your Athens details to view the article.