This essay presents a taxonomy that distinguishes among different categories of theories, models, and frameworks used in implementation science. The essay describes five categories of theoretical approaches that achieve three overarching aims: 1) process models, which are aimed at describing and/or guiding the process of translating research into practice; 2) determinant frameworks; 3) classic theories; 4) implementation theories, which are aimed at understanding and/or explaining what influences implementation outcomes; and 5) evaluation frameworks, which are aimed at evaluating implementation. Awareness of how the approaches differ is important to facilitate the selection of relevant approaches. Most determinant frameworks provide limited “how-to” support for carrying out implementation endeavours since the determinants usually are too generic to provide sufficient detail for guiding implementation. And while the relevance of addressing barriers and enablers to implementation is mentioned in many process models, these models do not describe specific determinants associated with implementation success.