Sharon Kulko Horn (plaintiff) and Ezra Kulko (defendant) were residents of New York who married in California, in 1959, during a brief stopover as Kulko traveled to Korea for military duty. Upon the termination of Kulko’s military service, the couple lived together in New York for 13 years, during which time they had a son and a daughter. After separating, Horn moved to California. She returned briefly to New York, however, to sign a separation agreement in which the couple agreed to joint custody: the children would reside in New York during the school year and in California during summer and holiday vacations. Kulko was to pay $3,000 in child support annually to cover the periods during which the children resided with Horn. After entering the separation agreement, Horn traveled to Haiti and there obtained a divorce that incorporated the separation agreement. In 1973, the couple’s daughter sought to live with Horn during the school year. Kulko bought her a one-way ticket to California, and from then on, the girl spent the school year in California and vacations in New York. In 1976, the couple’s son told Horn he wanted to live in California as well. Horn bought him a plane ticket and he relocated. One month later, Horn moved a California court for recognition of the Haitian divorce decree as a California judgment, for full custody of the children, and for an increase in child support. Kulko challenged the court’s personal jurisdiction over him, but the court ruled that it could exercise jurisdiction based solely on Kulko’s act of sending the daughter to California. He appealed.