Changes in fertility for the 46 prefectures of Japan are traced from 1920 to 1965, using census and vital statistics. During the period, substantial declines were recorded in both marital-fertility levels and the proportions of women of childbearing age who were married. Regional variation is pronounced in the timing of the onset of the decline in marital fertility. Only in the most industrialized districts did marital fertility begin to fall before 1950; thereafter, sharp declines were recorded in all parts of Japan. The marriage proportion, in contrast, was falling rather steadily throughout the islands between 1920 and 1950, after which the proportion stabilized. The decline in overall fertility that occurred before 1950was caused, then, primarily by a reduction in the proportion married; only after 1950 did a decline in marital fertility become a. major factor. The time pattern of change in marital-fertility levels and proportions married for Japan differs from that observed in western Europe, where low proportions married are recorded in the earliest national censuses. Apparently a fall in proportions married in western Europe preceded by one or two centuries the major sustained declines in marital fertility that were part of the so-called demographic transition.