It covers R6RS. Edit: More specifically, quoting from the book's site at MIT Press (http://mitpress.mit.edu/catalog/item/default.asp?ttype=2&tid=11984 http://m

It covers R6RS. Edit: More specifically, quoting from the book's site at MIT Press (http://mitpress.mit.edu/catalog/item/default.asp?ttype=2&tid=11984 http://mitpress.mit.edu/catalog/item/default.asp?ttype=2&#38...): The fourth edition has been substantially revised and expanded to bring the content up to date with the current Scheme standard, the Revised6 Report on Scheme. All parts of the book were updated and three new chapters were added, covering the language's new library, exception handling, and record-definition features.