Three-dimensional　(3D)　printing　has　revolutionized　the　world　manufacturing　production.　In　biomedical　applications,　however,　3D　printed　constructs　fell　short　of　expectations　mainly　due　to　their　inability　to　adequately　mimic　the　dynamic　human　tissues.　To　date,　most　of　the　3D　printed　biomedical　structures　are　largely　static　and　inanimate　as　they　lack　the　time-dependant　dimension.　To　adequately　address　the　dynamic　healing　and　regeneration　process　of　human　tissues,　4D　printing　emerges　as　an　important　development　where　＂time＂　is　incorporated　into　the　conventional　concept　of　3D　printing　as　the　fourth　dimension.　As　such,　additive　manufacturing　(AM)　evolves　from　3D　to　4D　printing　and　in　the　process　putting　stimulus-responsive　materials　in　the　limelight.　In　this　review,　the　state-of-the-art　efforts　in　integrating　the　time-dependent　behaviour　of　stimulus-responsive　materials　in　4D　printing　will　be　discussed.　In　addition,　current　literatures　on　the　interactions　between　various　types　of　stimuli　(categorized　under　physical,　chemical　and　biological　signals)　with　the　associated　stimulus-responsive　materials　will　be　the　major　focus　in　this　review.　Lastly,　potential　usage　of　4D　printing　in　biomedical　applications　will　also　be　discussed,　followed　by　technical　considerations　as　well　as　outlook　for　future　discoveries.　Statement　of　Significance　In　this　Review,　we　have　demonstrated　the　significance　of　4D　printing　in　biomedical　applications,　in　which　＂time＂　has　been　incorporated　into　the　conventional　concept　of　3D　printing　as　the　4th　dimension.　As　such,　4D　printing　differentiates　and　evolves　from　3D　printing　using　stimulus-responsive　materials　which　can　actively　respond　to　external　stimuli　and　more　sophisticated　＂hardware＂-printer　which　can　achieve　multi-printing　via　mathematical-predicted　designs　that　are　programmed　to　consider　the　transformation　of　3D　constructs　over　time.　The　emphasize　will　be　on　the　interactions　between　various　types　of　stimuli　(categorized　under　physical,　chemical　and　biological　signals)　with　the　associated　stimulus-responsive　materials,　followed　by　technical　considerations　as　well　as　outlook　for　future　discoveries.　(C)　2019　Acta　Materialia　Inc.　Published　by　Elsevier　Ltd.　All　rights　reserved.