ROOK Rook is a system for authoring descriptive grammars in HyperCard for the Macintosh. It is a tool for interactively and incrementally developing a grammar description based on an interlinear text corpus (as produced by SIL's IT program). The resulting on-line descriptive grammar exploits the capacity of the computer to provide instant access to cross-referenced topics, text examples, explanations of morpheme glosses, and so on. System requirements: HyperCard 2.0 or later, Mac system 6.0.5 or later. SIL's IT (interlinear text) program is recommended. J. Randolph Valentine valentin@julian.uwo.ca