The 2011 Kidney Disease: Improving Global Outcomes (KDIGO) Clinical Practice Guideline for Acute Kidney Injury (AKI) aims to assist practitioners caring for adults and children at risk for or with AKI, including contrast-induced acute kidney injury (CI-AKI). Guideline development followed an explicit process of evidence review and appraisal. The guideline contains chapters on definition, risk assessment, evaluation, prevention, and treatment. Definition and staging of AKI are based on the Risk, Injury, Failure; Loss, End-Stage Renal Disease (RIFLE) and Acute Kidney Injury Network (AKIN) criteria and studies on risk relationships. The treatment chapters cover pharmacological approaches to prevent or treat AKI, and management of renal replacement for kidney failure from AKI. Guideline recommendations are based on systematic reviews of relevant trials. Appraisal of the quality of the evidence and the strength of recommendations followed the GRADE approach. Limitations of the evidence are discussed and specific suggestions are provided for future research.