What is the lithosphere? What things subduct, what things do not, and why? How is the lower continental crust formed? Where are the large-ion lithophile elements stored? Is the style of plate tectonics episodic? These and related questions were considered during a workshop held at the University of Texas at Austin in March 1982 under the sponsorship of the U.S. Geodynamics Committee (USGC). The objectives of the workshop were somewhat unusual in that participants were asked to identify assumptions underlying proposed models and hypotheses, with special emphasis on controversies inherent in the various models. No attempt was made to reach consensus. The flavor of the discussions is indicated by the questions above, devised by a steering committee, each serving as the point of departure for approximately one half day of the wide-ranging discussion.