We present an interactive approach for helping designers describe, revise, analyze, and illustrate assemblies of mechanical parts within the context of a common data structure and set of assembly features. This paper describes an implementation used to test the validity of these ideas, which has been integrated into an existing spline-based geometric modeling system.Several interactive tools have been implemented. An assembly planner allows the user to design the assembly structure before modeling any geometry by using a combination of top-down and bottom-up design. After the geometry of each part in the assembly, together with its assembly features, has been modeled, the user can interactively put the parts together and perform degree of freedom analysis on them by using another tool. Such an interactive approach can help a designer determine whether the design is sound before the entire assembly is put together. Finally, once all part connections have been established, an exploded view generation tool can help the designer create an informative illustration of the product for the purposes of documentation or further visual analysis.