The Interdisciplinary Conceptual Design of Buildings Design activity during the conceptual phase of building projects is dynamic, vibrant and as a result, chaotic in appearance. This problem is compounded by the fact that iterative, or cyclic, design progression is often criticised, with the concept of 'going round in circles' being one that is discouraged. However, designbis a learning activity and, owing to the complexity of contemporary building projects,it is often only by moving ahead to improve knowledge, before taking a step back to re-address a problem with improved understanding, that the design process can progress. Today's design professionals are being urged to undertake early design activity in a more programmable, and thus manageable fashion. As such, it is becoming increasingly apparent that designers have little, if any, shared understanding of what conceptual design actually involves, let alone a deeper knowledge of the structure of iterative progression. This can, and is, causing problems for the industry, as the lack of both common understanding and synchronisation in interdisciplinary thinking is resulting in design team fragmentation and adversarial relationships. By modelling design activity it is possible to simplify, and thus ease understanding of, its complexities. The development and trialling of a generic framework of design phases and activities has allowed a simple graphical means of recording and displaying patterns of design progression to be devised. The models produced have been used to study and analyse the patterns of iterative working, the output of which has enabled a clarification of conceptual design practice to be achieved. A web-based design system has been developed from the paper-based framework. This accords well with the richly iterative and often non-linear process which design typically follows and is intended to encourage creativity without imposing a rigid procedure. The tool offers alternative routes through conceptual design, and contains 'Team Thinking Tools' to help designers widen the solution space, set priorities and evaluate options. In addition, it promotes effective teamwork practices to help teams deal with social interactions. Also, at the user's option, the system can be used to capture, store and retrieve decisions made, and the reasoning behind them. This is of key importance in improving the performance of the industry as a whole, for it is only by understanding how the final product is influenced by early design activity, that the design process can be adapted to take account of these issues on future projects.