Most methodologies deal with the design and the implementation of an individual system. Traditionally SDL is used to describe the functional properties of one system; from the SDL description a concrete system is derived which implements the defined functionality. In the ESPRIT project PROTEUS, we wanted to support evolving systems i.e. a family of systems from which various instances can be adapted. The PROTEUS Configuration Language, PCL, is a notation for describing and controlling variability. Using PCL, it is also possible to describe files and tools which are used to build executable systems. PCL tools and a flexible SDL code generator support automate system building. This paper presents how we use PCL together with SDL to model variability and automated system building. 1. INTRODUCTION Most methodologies deal with the development of individual systems. However, software products seldom live unchanged after their initial creation. They are typically adapted according to the ne..