CSL is a programming language designed for use in the field of complex logical problems. The basic approach adopted is that groups of items or objects sharing similar qualities can best be represented intensively, by recording the names of these items in predicative groups or sets, rather than by listing them extensively and coding their qualities numerically. The first application of the language has been in the field of Monte Carlo simulation work, for which special facilities are provided. An unusual compilation approach has been followed, involving translation into FORTRAN as an intermediate stage.