More than 1200 diterpenes have been identified from approximately 550 Compo sitae taxa (Figure 1 [pp. 219-384], Tables 1-3 [pp. 7-218]). The annual output of such reports rose sharply during the past several years, a trend that was also reflected by other major lipophilic constituents of the Compositae: acetylenes (63, 465), sesquiterpene lactones (266, 458), and benzofurans and chromenes (429). Unlike these other natural products, no review of the diterpene chemistry of the Compositae has been published. Given the bulk of data currently on hand, a review of this topic is clearly overdue. Several major goals influenced the preparation of this review. The first was to provide a useful reference to guide terpenoid chemists to the literature of known compounds. The published reports for 1200 structures provide a sizable body of spectroscopic data applicable to the investigation of new compounds. The study of diterpenes has been hampered by the absence of an all-inclusive nomenclature and classification system for the various skeletal types. Conse­ quently, a second goal was to organize structural data into a classification scheme designed to group compounds by biogenetic homology, and to standardize such features as diterpene nomenclature and numbering. Pursuant to this goal, the published names (Table 1) and numbering systems (Table 2) for all compounds are included.