This article presents a history of the origins and development of the AMA Guides to the Evaluation of Permanent Impairment (AMA Guides), from the publication of an article titled “A Guide to the Evaluation of Permanent Impairment of the Extremities and Back” (1958) until a compendium of thirteen guides was published in book form in 1971. The most recent, sixth edition, appeared in 2008. Over time, the AMA Guides has been widely used by US states for workers’ compensation and also by the Federal Employees Compensation Act, the Longshore and Harbor Workers’ Compensation Act, as well as by Canadian provinces and other jurisdictions around the world. In the United States, almost twenty states have developed some form of their own impairment rating system, but some have a narrow range and scope and advise evaluators to consult the AMA Guides for a final determination of permanent disability. An evaluator's impairment evaluation report should clearly document the rater's review of prior medical and treatment records, clinical evaluation, analysis of the findings, and a discussion of how the final impairment rating was calculated. The resulting report is the rating physician's expert testimony to help adjudicate the claim. A table shows the edition of the AMA Guides used in each state and the enabling statute/code, with comments.