The Electronic Cocktail Napkin is an experimental computer-based environment for sketching and diagramming in conceptual design. The project's goal is to develop a computational drawing environment to support conceptual designing in a way that leads smoothly from diagrams to more formal and structured representations of schematic design. With computational representations for conceptual designs, computer-supported editing, critiquing, analysis, and simulation can be employed earlier in the design process, where it can have a greater impact on outcomes. The paper describes the Electronic Cocktail Napkin program - its recognition and parsing of diagrams and management of spatial constraints, its drawing environment, and two experimental query-by-diagram schemes for retrieving information from architectural databases.