Trygve Nagell or Trygve Nagel (13 July 1895 – 24 January 1988) was a Norwegian mathematician, known for his works on Diophantine equations in number theory.

[3] He received his doctorate at the University of Oslo in 1926, where his advisor was Axel Thue.

[2] His doctoral students include Harald Bergström.

[4] The Nagell–Lutz theorem is a result in the Diophantine geometry of elliptic curves, which describes rational torsion points on elliptic curves over the integers.

It was published independently by Nagell and by Élisabeth Lutz.