Pages 220-279 of the International Code of Botanical Nomenclature (1956) are occupied by a list of conserved and rejected names of genera of Spermatophyta. The origins and history of conservation have been discussed by Stafleu (Taxon 5: 85-95). As a result of his study it became evident that the list is no longer in harmony with current concepts of nomenclature and the rules for maintaining them. The desirability of a general revision of the list is obvious; such a revision was begun by Stafleu several years ago. It proved, however, an impossible task for one person to achieve in the intervals between ordinary duties. Consequently application was made by The International Association for Plant Taxonomy to the National Science Foundation (Washington) for a grant in furtherance of this project. The grant was awarded early in 1958, enabling the present authors to work together for some seven weeks in Holland and England, principally in the Institute of Systematic Botany of the University of Utrecht and the Botany Department of the British Museum (Natural History). During this period we completed the verification (begun by Stafleu alone) of almost every citation in the list, and the evaluation of every conservation and rejection in the light of the current rules of nomenclature. The final manuscript was prepared later, in Utrecht and New York; an additional conference of the authors was made possible by Stafleu’s visit to the United States in December, 1958. A proposal has been presented to the Ninth International Botanical Congress, to be held at Montreal in 1959, to replace the current list of conserved and rejected names of genera of Spermatophyta by a new list based on that which follows (see Synopsis of Proposals, Regnum Vegetabile 14: 79. 1959).