Josephus (Sepp) Koster (born 17 September 1974 in Heemskerk) is a former Dutch racing driver.

The young driver continued racing while studying mechanical engineering at the Eindhoven University of Technology.

While Bas Leinders won the championship, Koster achieved a third place in the standings after his inaugural autoracing season.

Driving a Swift he participated in the Formula Ford Festival achieving a 17th place in the championship race.

With all drivers racing equal Reynard Formula Opel/Vauxhall cars the couple achieved a sixth place at the 1996 EFDA Nations Cup.

At the 1997 EFDA Nations Cup, again coupled with Sandor van Es, the duo reached a ninth place.

[5] The Dutch driver finished his first season in the Barber Dodge series in ninth place of the championship.

After Todd Snyder passed him on the tight street circuit Koster settled for second place.

Being fast all weekend long Koster won the race at Nazareth Motor Speedway.

[11] After scoring his first top ten finish at Long Beach Koster had to withdraw from the Milwaukee race.

After a crash during practice on Friday Kosters Swift 014.a was too badly damaged to race on Sunday.