1 Introduction.- 1.1 What is a mechanism?.- 1.2 Where does evidence of a mechanism come from?.- 1.3 Why consider evidence of mechanisms?.- 1.3.1 Evaluating efficacy.- 1.3.2 Evaluating external validity.- 1.3.3 Other questions.- 1.3.4 Importance of considering evidence of mechanisms.- 2 How to consider evidence of mechanisms: a summary.- 2.1 Questions to address.- 2.2 Quality level of evidence and status of claim.- 2.3 Identifying evidence of mechanisms in the literature.- 2.4 Evaluating evidence of mechanisms.- 2.5 Using evidence of mechanisms to evaluate causal claims.- 2.6 Overall approach.- 3 Identifying evidence of mechanisms in the literature.- 3.1 Hypothesize a mechanism.- 3.2 Search the literature.- 3.3 Identify the evidence most relevant to the mechanism hypothesis.- 3.4 Presenting the evidence of mechanisms.- 4 Evaluating evidence of mechanisms.- 4.1 Considerations for evaluating evidence of mechanism.- 4.2 Presenting quality of evidence of mechanisms.- 5 Using evidence of mechanisms to evaluate efficacy and external validity.- 5.1 Efficacy.- 5.2 External validity.- 6 Glossary.- 7 References.- 8 Acknowledgements.- 9 Appendix A. A critical appraisal tool for evidence of mechanisms.- 10 Appendix B. GRADE tables with mechanism assessment.- 11 Appendix C: Databases for evidence of mechanisms.- 12 Appendix D: Assessing exposures.- 12.1 Example: carcinogenicity of benzo[a]pyrene.- 12.2 Comparison to IARC.- 12.3 Molecular epidemiology.- 12.4 Comparison to SYRINA.