 This paper examined the use of theory in implementation research from 1966 to 1998. It found that only 22.5% of the studies included a theoretical framework or model. Most studies used only one theory, with the most common being precede, predisposing, reinforcing, and enabling constructs in educational diagnosis and evaluation, diffusion of innovations, information overload and social marketing, academic detailing. Only a few studies used multiple theories. The authors concluded that there was poor justification of choice of intervention and use of theory in implementation research, until at least 1998. They recommended that future research should explicitly identify the justification for the interventions, as well as greater use of explicit theory to understand barriers, design interventions, and explore mediating pathways and moderators. This article was authored by Grimshaw Jeremy M, Walker and E, and Davies Philippa.