Abstract: The growth of the Internet and the advent of the computational "Grid" have made it possible to develop and deploy advanced computational collaboratories . These systems build on high-end computational resources and communication technologies underlying the Grid, and provide seamless and collaborative access to particular resources, services or applications. Integrating these "focused" collaboratories presents significant challenges. Key among these is the design and development of robust middleware support that addresses scalability, service discovery, security and access control, and interaction and collaboration management for consistent access. In this paper we first investigate the architecture of such a middleware that enables global (web-based) access to collaboratories. We then present the design and implementation of a middleware substrate that enables a peer-to-peer integration of and global (collaborative) access to geographically distributed instances of the DISCOVER computational collaboratory for interaction and steering.