Monika Cassens (née Thiere, born 28 February 1953) is a German former badminton player.
She started her career in Tröbitz. For this club she won 15 national titles. After her marriage to Claus Cassens, she changed to SG Gittersee, a badminton club in Dresden. During her career she won 101 international tournaments. She won 6 Polish Open titles in a row in women's singles and women's doubles, and six titles in mixed doubles. In 1990 she won the Malta International.