Born in Zaandam, Koeman began his career at Groningen before transferring to the Netherlands' most successful club Ajax in 1983, where he won the national Eredivisie title in 1984–85. He then joined Ajax's rivals PSV Eindhoven in 1986, winning three consecutive Eredivisie titles (1986–87, 1987–88 and 1988–89) and the European Cup in 1988. Ronald Koeman is one of five European players to ever win a treble with their club and a cup with their national team in the same year. The other four players are his teammates Hans van Breukelen, Berry van Aerle, Gerald Vanenburg and Wim Kieft. In 1989, Koeman moved to Barcelona and became part of Johan Cruyff's "Dream Team", helping the club win La Liga four years in a row between 1991 and 1994, and the 1991–92 European Cup, where he scored the winning goal of the final against Sampdoria.