When Richard Goldschmidt emigrated to the United States in 1936, he had influenced a whole generation of young biologists, and had stimulated their research by his revolutionary ideas. Stern (1967, see p. 21) called him: 'Contributor of permanent parts, some very large; preceptor and critic of his era; designer of frameworks for the future'. In 1958 Goldschmidt's obituary was prefaced by the following statement: 'Der nachstehende Nekrolog erscheint gleichzeitig in Science und Ex­ perientia, damit das universale Heimatrecht Richard Goldschmidts zum Ausdruck bringend. Die Leser von Experientia erinnern sich dankbar der verschiedenen genetischen Aufsiitze dieses immer anregenden Geistes, dem unsere Wissenschaft grosse Impulse verdankt.' (Translation: The following obituary appears simultaneously in Science and in Experientia, a symbol of Richard Goldschmidt's right to be called a world citizen. Readers of Experientia will recall with appreciation several of the papers of this highly stimulating author to whom our science owes a great deal. (Experientia 14, 307, 1958). In commemoration of the 20th anniversary of Richard Goldschmidt's death (April 24, 1958) and the 100th anniversary of his birth (April 12, 1878) Experientia presents a contemporary evaluation of several of Goldschmidt's major scientific theories. We believe that some of these theories were far ahead of his time and that the controversies which they aroused are of considerable didactic interest to biologists today. Further­ more, they represent an important chapter in the history of biology.