Workflow systems have come into recent vogue as an approach to supporting the co-ordination of business processes. The current surge of commercial activity in groupware and workflow software products has been triggered largely by the widespread use of business process re-engineering (BPR). While commercial products have developed to meet market opportunities, academic research has moved towards support for so-called transactional workflows, where workflow paradigms are applied to the mainstream of mission critical applications. This paper addresses the needs of the growing number of applications which cross the boundaries between organisations. Following a brief review of workflow developments, the needs of such cross-boundary applications are discussed. A model for operation of an appropriate workflow system is described, and the facilities of a "lightweight" workflow server are proposed.