The KNOBS [ENGELMAN 80] planning system is an experimental expert system which assists a user by instantiating a stereotypical solution to his problem. SNUKA, the natural language understanding component of KNOBS, can engage in a dialog with the user to allow him to enter components of a plan or to ask questions about the contents of a database which describes the planning world. User input is processed with respect to several knowledge sources including word definitions, scripts which describe the relationships among the scenes of the problem solution, and four production system rule bases which determine the proper database access for answering questions, infer missing meaning elements, describe how to conduct a conversation, and monitor the topic of the conversation. SNUKA differs from GUS [BOBROW 77], a dialog system similar to SNUKA in its goals, in its use of a script to guide the conversation, interpret indirect answers to questions, determine the referents of nominals, perform inferences to answer the user’s questions, and decide upon the order of asking questions of the user to maintain a coherent conversation. SNUKA differs from other script-based language understanders such as SAM [CULLINGFORD 78] and FRUMP [DEJONG 79] in its role as a conversational participant instead of a story understander.