Early years in Holland and attraction to astronomy; education at Groningen (1946-1949) and at Leiden under Oort (1949-1956); life at Hale Observatories and Caltech (1956-1977). Research on comets, radio map of galaxy, distribution of mass and rate of star formation in galaxy, red shifts of galaxies and quasars, nature of quasars. Views on cosmology, use of 200-inch telescope, and social relations of astronomy.