Olaf Janßen (born 8 October 1966) is a retired German footballer and manager, who played as a midfielder.

Janßen spent most of his playing career with German Bundesliga sides 1. FC Köln and Eintracht Frankfurt, where he later worked as a scout.

In September 2013 he was appointed as manager of Dynamo Dresden, but was sacked after nine months on the job.

In June 2016 Janßen became assistant coach to VfB Stuttgart head coach Jos Luhukay. From 15 to 20 September 2016 he was caretaker manager of the club. Janßen took on a new role as scout of VfB Stuttgart and left the coaching staff after the appointment of the new head coach Hannes Wolf.

For the 2017–18 season, he was appointed as the head coach of FC St. Pauli. He was sacked on 7 December 2017.

In January 2018 he became new manager of FC Viktoria Köln replacing Marco Antwerpen. He returned to Cologne on 1 February 2021. After four years, he was signed by SV Sandhausen.

Janßen played for West Germany at the 1988 Summer Olympics in Seoul.