Abstract: A substrate aligner for a substrate carrier or cassette including an engagement assembly for moving and maintaining one or more substrates into an aligned position when closed, and an actuator assembly for opening and closing the engagement assembly. In one embodiment, the engagement assembly includes front and back engagement assemblies for mounting at opposite corners of the housing to thereby interface opposite comers of the substrates. Each engagement assembly preferably includes a roller for interfacing a corresponding edge of each the substrates, where the front assembly includes two rollers for interfacing front edges and adjacent side edges, and the back engagement assembly includes two rollers for interfacing the back edges and the opposite side edges of the substrates. In this manner, the engagement assembly interfaces all four edges of each substrate to thereby manipulate and maintain the substrates into a substantially aligned position when closed.