As a distillation of the architectural proposition, the diagram, model or concept sketch is a critical component in the design process of the architect. The process of making a diagram, drawing, model or ‘drawing forth’ a design helps to define a project and to clarify the conceptual idea or strategy. Through this activity the design intent for a given architectural project takes form through processes of iteration, substitution, abstraction, clarification leading to the articulation of an architectural proposition. This thesis investigates the efficacy of the architect’s ‘diagram’ as a tool in the design process leading to poetic thinking, and the relationship between theory and this process. Of necessity the diagram, model or concept sketch, a visual form of communication, holds information intrinsic to the project; geographic, topographic and climatic site conditions, programmatic and historical and cultural context. The material an architect draws on to inform this preliminary activity ranges from information drawn from observation, analyses and documentation of empirical data to cross disciplinary theories, intuitions and memories of previous experience. Together information and disciplinary knowledge provide a framework with which to explore the potential poetics of a project and its specific architectural proposition. This study will focus on a detailed analysis of the diagram, that which preceeds the built form as opposed to a retrospective production, enabling the investigation of the generation of ideas, through the work of two architectural practices and their respective processes. Central to the thesis is an interrogation of the design process through the use of the diagram by Steven Holl and Rem Koolhas/OMA. Holl and Koolhaas have been selected for their distinctively different approaches to the use of the diagram and their respective pre-dispositions on theory and design methodology. Through analysis, it will be argued, the diagram, sketch or model, empirical analysis and interrogation of site, culture, and grounds at play, is the place of discovery or emergence of ‘idea.’ This thesis seeks to investigate how, through the diagram, sketch or model, information and ideas are negotiated and ordered contributing to the design process activity which is core to the practice of making architecture. Through this analysis questions of the relevance, meaning and potential of the diagram are raised. To what extent does the information held in the diagram, concept sketch or model, inform architecture of its time and place? Are design ideas and theoretical positions relating to grounding of architecture in place and time evidenced in the diagrams of Steven Holl and Rem Koolhaas? This thesis will seek to investigate the efficacy of the diagram and its potential to guide the process leading to architectural propositions.