In addition to contributing a specification of Scheme, this paperpresents several novel modeling techniques for Felleisen Hieb-style rewriting semantics that we discovered while developing our R5RSScheme semantics. All are applicable to a wider range of problems than the specific uses we have for them, and the fact that theycombine seamlessly in our full R5RS model shows that they scale to real languages. 1. Introduction The Revised5 Report on the Algorithmic Language Scheme ,R5RS, provides an informal, English specification of Scheme and a denotational model of a core Scheme language. The denota-tional specification is more precise than the informal specification, but is also incomplete with respect to it. For instance, the formalspecification does not present the top-level mentioned throughout the informal specification, and is missing key procedures such asdynamic-wind and eval whose inclusion could have a significant impact on the formalism. While that is not necessarily a problem-- the measure of a model is not its completeness but its ability to clearly and accurately explain its subject-- Gasbichler et al's re-cent explanation of the difficulties involving dynamic contexts and threads , for instance, demonstrate that the formal model is in-sufficient for some important questions.