CATPAC - An interactive software package for control system design. This report describes a dialogue-oriented software package for computer- aided engineering in control instrumentation. It comprises programmed algorithms for process identification, analysis, simulation, and controller design. For this package a novel architecture was developed to enable a userfriendly interactive application of algorithms. The special structure of the system supports the archiving of computed results, and it facilitates the selection of suitable methods by providing interactive aids.