In this paper, we report about the designl development, and implementation of the SEPIA cooperative hypermedia authoring environment. It provides results on the following aspects of SEPIA: persistent and shared data storage, hypermedia data model with composites, sophisticated and comprehensive authoring functionality, support for anew rhetoric and for cooperative work. We start by identifying the challenge of hypermedia authoring and production which serves asthe driving force for our development. Using interacting problem spaces as the vehicle for modelling the dynamic aspects of authoring, we arrive at a set of requirements answered by the concept of “activity spaces”. The design of coherent hyperdocuments is facilitated by our “construction kit”. Furthermore, we describe the extensions and modifications necessary to suppok multiple authors with the cooperative version of SEPIA. The central issue of the paper is the system architecture and its implementation. We describe the basis for access to shared hyperdocuments, the activity space browsers, the integration of multimedia functionality(audio, graphics, pictures), and the integration of a video conferencing system.