The problem of the layout of multi-product lines is considered as an integral part of production system planning. The paper discusses the stages in production system planning and identifies five types of system. The layout of multi-product lines involves determining the number of stations in the line, the machine type at each station, and the station at which each operation is to be performed. The problem is described in the context of work flow and work load. A special case, the single machine case, is identified and some methods for its solution discussed. A procedure for solution of the general case is proposed, consisting of these stages: construction of a line with uni-directional flow; elimination of uneconomic work stations; and simulation of alternative line configurations. The method is illustrated by a case study.