**Kai Behrend** is a German mathematician. He is a professor at the University of British Columbia in Vancouver.

His work is in algebraic geometry and he has made important contributions in the theory of algebraic stacks, Gromov–Witten invariants and Donaldson–Thomas theory (cf. Behrend function.) He is also known for Behrend's formula, the generalization of the Grothendieck–Lefschetz trace formula to algebraic stacks. He is the recipient of the 2001 Coxeter–James Prize, the 2011 Jeffery–Williams Prize, and the 2015 CRM-Fields-PIMS Prize.

Gromov-Witten Invariants in algebraic geometry, Inventiones Mathematicae, vol. 127, 1997, pp. 601-617, Arxiv
with Barbara Fantechi: The intrinsic normal cone, Inventiones Mathematicae, vol. 128, 1997, pp. 45-88, Arxiv
with Yuri Manin: Stacks of stable maps and Gromov Witten Invariants, Duke Mathematical Journal, vol. 85, 1996, pp. 1-60, Arxiv
Derived ℓ-adic categories for algebraic stacks, Memoirs of the American Mathematical Society, 2003, MR1963494