This paper describes current problems in the field of assembly planning and reasons why industrial enterprises need integrated, computer aided tools for the design of worksystems. An example of such a tool is presented in this article. With this computer aided planning system (CAP) called EMMA (expert for the design of manual assembly workplaces ≡ Experte zur Gestaltung manueller Montagear-beitsplätze), it is possible to plan ahead a workplace considering all anthropometrical and biomechanical restrictions, based on a geometric design model of the product, that has to be assembled. A combination of heuristics is used to achieve the objectives of the planning process. Taken into account are the economic aspects as well as human factors. A multi dimensional evaluation of the planning solution and the interactive optimization will lead to workplaces of high economic and ergonomic value. At the end of the article, a case study describes how EMMA works.