Evidence of mechanisms plays an important role in medical decision‐making, but this role is less well articulated than that of clinical trial evidence. A new book, Evaluating Evidence of Mechanisms in Medicine: Principles and Procedures, provides a framework and resources for explicitly evaluating evidence of mechanisms when assessing claims of efficacy and external validity. This review outlines the overall approach of the book, the contribution it makes to evidence evaluation in medicine and makes some suggestions for further work that will aid implementation of the framework into clinical decision‐making.