An information recording medium, a recording/reproducing method and apparatus, and a host apparatus are provided to ensure compatibility between information recording media having functions of a new standard and existing standard drive systems. The information recording medium includes a data area, a defect management area for managing a defect occurring in the data area, and an access control area in which access control data regarding a recognizable function by a recording/reproducing apparatus into which the medium is loaded and access control data regarding an unrecognizable function by the recording/reproducing apparatus are recorded, wherein a write protection flag recorded in the defect management area and the access control data recorded in the access control area provide reinitialize verification information for verifying whether the medium is reinitializable.