The present invention relates to a rotating and sliding boat boarding door mechanism configured to aid the vessel's occupants in their ingress and egress to and from the vessel. More particularly, the present invention provides a rotating and sliding boat boarding door assembly and system that slidingly moves into a recess in the vessel's exterior (e.g., side, transom, and/or gunwale) that has been configured to receive and maintain the boarding door assembly in a position where it is out of sight when fully recessed.