A key challenge in Grid Computing is the ability to create reliable and scalable virtual organisations (VOs) which operate in an open, dynamic and competitive environment. In response, in the CONOISE-G project, we are developing an infrastructure to support robust and resilient virtual organisation formation and operation. Specifically, CONOISE-G provides mechanisms to assure effective operation of agent-based VOs in the face of disruptive and potentially malicious entities in dynamic, open and competitive environments. In this paper, we describe the architecture of the CONOISE-G system, and provide details of its implementation.