Software engineering is a fundamentally collaborative activity, yet most tools that support software engineers are designed only for single users. There are many foreseen benefits in using tools that support real time collaboration between software engineers, such as avoiding conflicting concurrent changes to source files and determining the impact of program changes immediately. Unfortunately, it is difficult to develop non-trivial tools that support real time Collaborative Software Engineering (CSE). Accordingly, the few CSE tools that do exist have restricted capabilities. Given the availability of powerful desktop workstations and recent advances in distributed computing technology, it is now possible to approach the challenges of CSE from a new perspective. The research goal in this thesis is to investigate mechanisms for supporting real time CSE, and to determine the potential gains for developers from the use of CSE tools. An infrastructure, CAISE, is presented which supports the rapid development of real time CSE tools that were previously unobtainable, based on patterns of collaboration evident within software engineering. In this thesis, I discuss important design aspects of CSE tools, including the identification of candidate patterns of collaboration. I describe the CAISE approach to supporting small teams of collaborating software engineers. This is by way of a shared semantic model of software, protocol for tool communication, and Computer Supported Collaborative Work (CSCW) facilities. I then introduce new types of synchronous semantic model-based tools that support various patterns of CSE. Finally, I present empirical and heuristic evaluations of typical development scenarios. Given the CAISE infrastructure, it is envisaged that new aspects of collaborative work within software engineering can be explored, allowing the perceived benefits of CSE to be fully realised.