We classify the existent Birkhoff-type theorems into four classes:First, in field theory, the theorem states the absence of helicity 0-and spin 0-parts of the gravitational field. Second, in relativistic astrophysics, it is the statement that the gravitational far-field of a spherically symmetric star carries, apart from its mass, no information about the star; therefore, a radially oscillating star has a static gravitational far-field. Third, in mathematical physics, Birkhoff's theorem reads:up to singular exceptions of measure zero, the spherically symmetric solutions of Einstein's vacuum field equation with Λ = 0 can be expressed by the Schwarzschild metric; for Λ = 0, it is the Schwarzschild-