Felix A. Theilhaber, a physician, was born in Germany in 1884 and died in Israel in 1956. He was a pioneer sexologist, demographer, and sportsman and an early Zionist. Theilhaber was an original thinker and a prolific writer. He fought courageously against the pervasive reactionary and antisocial attitudes in the Germany of his time and campaigned actively, in his public addresses, books, pamphlets, and papers, for sexual reform, especially for liberalization of abortion and legalization of contraception. He founded the Society for Sexual Reform (Gesex) in 1913 and was cofounder and sexologic adviser of one of the first birth control and sex advisory clinics in Berlin (1930), operating under the patronage of the Gesex. In 1925, he founded the Coalition for Reform of the (Germany) Criminal Law, and in 1928, the periodical Sexual Hygiene. Among 20 books authored by Theilhaber are The Decline of the German Jews (1911), Das Sterile Berlin (1913), and Goethe, Sexus and Eros (1929). After his emigration to Israel in 1935, he continued his writings and later founded a Health Insurance Company in Tel Aviv, acting as its medical director. He has left a great legacy for sexology.