He began his professional career in 1987 and spent time with Finnish clubs Reipas (1987-90), HJK (1991), and MyPa (1992) before joining Ajax, where he rose to international prominence. Between 1992 and 1999, he scored 135 goals in 253 appearances or Ajax, winning four league titles and the 1995 Champions League final (he finished as the tournament's second-highest scorer, with 6 goals).
After leaving Ajax, he one and a half relatively quiet seasons with Barcelona, then joined Liverpool in January 2001. In his first season there, he collected four trophies--the UEFA Cup, the UEFA Super Cup, the FA Cup, and the League Cup--then won a fifth--the Community Shield--at the start of the next season.
He returned to Ajax in 2002 and won another league title in 2004, then moved again to a series of clubs that included Lahti (2004, 2008-10), Hansa Rostock (2004-05), Malmö (2005-07), and Fulham (2007-08) before moving to his current club, HJK, in 2011 at the age of 40. Along the way, he made 137 appearances for Finland from 1989 to 210, scoring a record 32 goals.