The　ankle　joint　complex　(AJC)　is　of　fundamental　importance　for　balance,　support,　and　propulsion.　However,　it　is　particularly　susceptible　to　musculoskeletal　and　neurological　injuries,　especially　neurological　injuries　such　as　drop　foot　following　stroke.　An　important　factor　in　ankle　dysfunction　is　damage　to　the　central　nervous　system　(CNS).　Correspondingly,　the　fundamental　goal　of　rehabilitation　training　is　to　stimulate　the　reorganization　and　compensation　of　the　CNS,　and　to　promote　the　recovery　of　the　motor　system＇s　motor　perception　function.　Therefore,　an　increasing　number　of　ankle　rehabilitation　robots　have　been　developed　to　provide　long-term　accurate　and　uniform　rehabilitation　training　of　the　AJC,　among　which　the　parallel　ankle　rehabilitation　robot　(PARR)　is　the　most　studied.　The　aim　of　this　study　is　to　provide　a　systematic　review　of　the　state　of　the　art　in　PARR　technology,　with　consideration　of　the　mechanism　configurations,　actuator　types　with　different　trajectory　tracking　control　techniques,　and　rehabilitation　training　methods,　thus　facilitating　the　development　of　new　and　improved　PARRs　as　a　next　step　towards　obtaining　clinical　proof　of　their　rehabilitation　benefits.A　literature　search　was　conducted　on　PubMed,　Scopus,　IEEE　Xplore,　and　Web　of　Science　for　articles　related　to　the　design　and　improvement　of　PARRs　for　ankle　rehabilitation　from　each　site＇s　respective　inception　from　January　1999　to　September　2020　using　the　keywords　＂　parallel＂,　＂　ankle＂,　and　＂　robot＂.　Appropriate　syntax　using　Boolean　operators　and　wildcard　symbols　was　utilized　for　each　database　to　include　a　wider　range　of　articles　that　may　have　used　alternate　spellings　or　synonyms,　and　the　references　listed　in　relevant　publications　were　further　screened　according　to　the　inclusion　criteria　and　exclusion　criteria.Ultimately,　65　articles　representing　16　unique　PARRs　were　selected　for　review,　all　of　which　have　developed　the　prototypes　with　experiments　designed　to　verify　their　usability　and　feasibility.　From　the　comparison　among　these　PARRs,　we　found　that　there　are　three　main　considerations　for　the　mechanical　design　and　mechanism　optimization　of　PARRs,　the　choice　of　two　actuator　types　including　pneumatic　and　electrically　driven　control,　the　covering　of　the　AJC＇s　motion　space,　and　the　optimization　of　the　kinematic　design,　actuation　design　and　structural　design.　The　trajectory　tracking　accuracy　and　interactive　control　performance　also　need　to　be　guaranteed　to　improve　the　effect　of　rehabilitation　training　and　stimulate　a　patient＇s　active　participation.　In　addition,　the　parameters　of　the　reviewed　16　PARRs　are　summarized　in　detail　with　their　differences　compared　by　using　figures　and　tables　in　the　order　they　appeared,　showing　their　differences　in　the　two　main　actuator　types,　four　exercise　modes,　fifteen　control　strategies,　etc.,　which　revealed　the　future　research　trends　related　to　the　improvement　of　the　PARRs.The　selected　studies　showed　the　rapid　development　of　PARRs　in　terms　of　their　mechanical　designs,　control　strategies,　and　rehabilitation　training　methods　over　the　last　two　decades.　However,　the　existing　PARRs　all　have　their　own　pros　and　cons,　and　few　of　the　developed　devices　have　been　subjected　to　clinical　trials.　Designing　a　PARR　with　three　degrees　of　freedom　(DOFs)　and　whereby　the　mechanism＇s　rotation　center　coincides　with　the　AJC　rotation　center　is　of　vital　importance　in　the　mechanism　design　and　optimization　of　PARRs.　In　addition,　the　design　of　actuators　combining　the　advantages　of　the　pneumatic-driven　and　electrically　driven　ones,　as　well　as　some　new　other　actuators,　will　be　a　research　hotspot　for　the　development　of　PARRs.　For　the　control　strategy,　compliance　control　with　variable　parameters　should　be　further　studied,　with　sEMG　signal　included　to　improve　the　real-time　performance.　Multimode　rehabilitation　training　methods　with　multimodal　motion　intention　recognition,　real-time　online　detection　and　evaluation　system　should　also　be　further　developed　to　meet　the　needs　of　different　ankle　disability　and　rehabilitation　stages.　In　addition,　the　clinical　trials　are　in　urgent　need　to　help　the　PARRs　be　implementable　as　an　intervention　in　clinical　practice.