Birkhoff's theorem may refer to several theorems named for the American mathematician George David Birkhoff:
Birkhoff's theorem (relativity) Birkhoff's theorem (electromagnetism) Birkhoff's ergodic theorem
It may also refer to theorems named for his son, Garrett Birkhoff:
Birkhoff–von Neumann theorem for doubly stochastic matrices Birkhoff's HSP theorem, concerning the closure operations of homomorphism, subalgebra and product Birkhoff's representation theorem for distributive lattices Birkhoff's theorem (equational logic), stating that syntactic and semantic consequence coincide