Bert Ruiter is a Dutch bass guitarist, record producer, and composer.
Ruiter was born in Amsterdam and grew up in Hilversum. When he was twelve he started playing guitar by ear; later he switched to bass guitar. In 1966 he began his career by replacing Dick Ankersmit as bass guitarist for The Caps, with singer Hans van Hemert and guitarist Roy Beltman. Afterwards, he played in the groups Fullhouse and the Jay-Jays.
In September 1971 he replaced Cyril Havermans as the bass guitarist in Focus. He remained with Focus until the group dissolved in 1978. He then joined Earth & Fire, the group in which his wife Jerney Kaagman (whom he married in 1974) sang. The two later left Earth & Fire, and Ruiter worked with Kaagman on her solo albums, gradually assuming more of a role as producer and arranger. In 1999 Ruiter rejoined Thijs van Leer and drummer Hans Cleuver with guitarist Menno Gootjes, for a new incarnation of Focus, but internal wrangling split the group after only a few live dates in Holland.