Contemporary business process systems are built to automate routine procedures. Automation demands well-understood domains, repetitive processes, clear organisational roles, an established terminology, and predefined plans. Knowledge work is not like that. Plans for knowledge intensive processes are elaborated and reinterpreted as the work progresses. Interactive process models are created and updated by the project participants to reflect evolving plans. The execution of such models is controlled by users and only partially automated. An interactive process system should - Enable modelling by end users, - Integrate support for ad-hoc and routine work, - Dynamically customise functionality and interfaces, and - Integrate learning and knowledge management in everyday work. This thesis reports on an engineering project, where an interactive process environment called WORKWARE was developed. WORKWARE combines workflow and groupware. Following an incremental development method, multiple versions of systems have been designed, implemented and used. In each iteration, usage experience, validation data, and the organisational science literature generated requirements for the next version.