A systematic review of the mechanical design of powered ankle–foot prostheses developed from 2000 to 2019 was conducted through database and manual searches. A total of ten English and two Chinese databases were searched using the same keywords. Moreover, information on commercialized prostheses was collected through a manual search. A total of 8729 publications were obtained from the database search, and 83 supplementary publications and 49 online product introductions were accumulated through the manual search. A total of 91 powered ankle–foot prostheses were extracted from 159 publications and online information after exclusion. The mechanical design characteristics of the prostheses were described briefly and compared after they were categorized into 11 subclassifications. This review revealed that a considerable number of powered ankle–foot prostheses were developed in the last 20 years. The development of such prostheses was characterized by alternative modes, that is, from pneumatic or hydraulic drivers to motorized drivers and from rigid transmissions to elastic actuators. This review contributes to the comprehensive understanding of current designs, which can benefit the combination of the advantages of and redundancy avoidance in future powered ankle–foot prostheses.