Systematic reviews are essential to produce trustworthy guidelines. To assess the certainty of a body of evidence included in a systematic review, the Grading of Recommendations Assessment, Development and Evaluation (GRADE) Working Group has developed an approach that is currently used by over 100 organizations, including the World Health Organization and the Cochrane Collaboration. GRADE provides operational definitions and instructions to rate the certainty of the evidence for each outcome in a review as high, moderate, low, or very low for the effects of interventions, prognostic estimates, values and preferences, test accuracy, and resource utilization. The assessment includes assessing risk of bias, imprecision, inconsistency, indirectness, and publication bias, the magnitude of effects, dose-response relations, and the impact of residual confounding and bias. Summary statistical information and assessments of certainty are presented in GRADE evidence summary tables, which can be produced using GRADE's official GRADEpro software tool (www.gradepro.org/). The evidence summary tables feed into the GRADE Evidence to Decision frameworks which guideline panels can use to produce recommendations.