ASPEN (Advanced System for Process Engineering) is a software system for computer-aided process design. ASPEN was developed at M.I.T. during the period 1976-1981 under the sponsorship of the Department of Energy and 55 industrial participants. There are four manuals and one computer tape describing the maintenance, use, and installation of ASPEN. The ASPEN System Administrator Manual is a two volume manual containing system maintenance and updating procedures and documentation of the ASPEN program code. Supplementary reference material is contained on the ASPEN On-Line Documentation computer tape. The System Administrator Manual is intended to serve as a reference manual and a maintenance manual for ASPEN support staff and as a programmer's guide for anyone writing a new model. At least one person at each ASPEN installation will require access to this manual.