This manual introduces NewYacc, a parser generator system built upon the original yacc system within Unix. NewYacc's principal extension is to provide users with a way to associate rewrite rules with individual productions in the language grammar. These rules are used to describe how the parse tree (which is saved in NewYacc but not in original yacc) should be traversed, plus users can easily control what action is performed at each node in the tree during their traversals. This provides users with great leverage in the construction of a variety of source to source translation tools. This manual assumes a general familiarity with original yacc. (Also cross-referenced as UMIACS-TR-90-141)