Why was the research in this thesis done? Recruitment of participants is an important part of trials, but the evidence that is available to help trialists make decisions is disjointed, and we are unsure if and how evidence is used by trialists when they are planning their recruitment strategies. This thesis aims to combine the evidence from studies that tested recruitment methods but did so in ways that means participants did not have an equal chance of receiving one method or another (i.e. allocation was not randomised), find out how trialists are currently using evidence to guide their recruitment planning, and to develop a resource to communicate evidence about effective recruitment methods. What was done? The project is made up of three linked studies: 1. A systematic review of non-randomised evaluations of strategies to improve recruitment of potential participants to randomised controlled trials; 2. An interview study designed to explore how trial staff use evidence in the process of developing and planning their recruitment strategies; 3. Generation and user testing of a resource to communicate recruitment evidence to trialists. What did the thesis find? Though the non-randomised literature is disjointed, there is a lot of it, and even when consolidated the body of work remains relatively useless to trialists who want help to guide their recruitment planning. Ultimately trialists should be using the literature based on randomised allocation (i.e. everyone has an equal chance of receiving the things being tested), and the research community needs to work hard to make improvements in the way we design, conduct and report findings from non-randomised studies. Very few participants in the interview study mentioned recruitment evidence from the literature, the majority preferred to ask colleagues what methods they would recommend based on their past experience. Trialists were conscious of the need to use evidence to support their decisionmaking around recruitment strategies, specifically from one published systematic review of randomised recruitment literature. Many explained that they had been meaning to read this review, but did not have time due to exceedingly long to do lists. I developed and user tested a new way of presenting the evidence held in this review, and feedback from trialists was positive; they preferred being able to consume information quickly, in simple language and without large blocks of text. What difference does this thesis make? This thesis adds to our understanding of how and what type of evidence is used by trialists to make decisions about their trial recruitment strategies, and highlights the need for trial process evidence to be communicated in more effective ways. Research to rigorously evaluate the effect of the communication method developed in this thesis is planned.