Background: Observational methodology is one of the most suitable research designs for evaluating fi delity of implementation, especially in complex interventions.However, the conduct and reporting of observational studies is hampered by the absence of specifi c guidelines, such as those that exist for other evaluation designs.This lack of specifi c guidance poses a threat to the quality and transparency of these studies and also constitutes a considerable publication hurdle.The aim of this study thus was to draw up a set of proposed guidelines for reporting evaluations based on observational methodology.Method: The guidelines were developed by triangulating three sources of information: observational studies performed in different fi elds by experts in observational methodology, reporting guidelines for general studies and studies with similar designs to observational studies, and proposals from experts in observational methodology at scientifi c meetings.Results: We produced a list of guidelines grouped into three domains: intervention and expected outcomes, methods, and results. Conclusions:The result is a useful, carefully crafted set of simple guidelines for conducting and reporting observational studies in the fi eld of program evaluation.