The file system for the Michigan terminal system (MTS) is described. MTS is a general-purpose multiprogramming multiprocessing paged time-sharing system for the IBM 360/67 and 370/168 developed at the University of Michigan, Ann Arbor. First, an overview of some of the external facilities provided to the users of files is presented; then some of the internal design philosophy and corresponding implementation strategy for the file system are discussed. Particular emphasis is placed on how the sharing of files is accomplished, both from the user's point of view and the system's point of view. A retrospective judgment of some of the strengths and weaknesses of the MTS file system is given. Finally, an appendix details the allowable concurrent usage of files and the algorithm used for file deadlock detection in MTS.