In quantum mechanics, an antisymmetrizer A (also known as antisymmetrizing operator) is a linear operator that makes a wave function of N identical fermions antisymmetric under the exchange of the coordinates of any pair of fermions. After application of A the wave function satisfies the Pauli exclusion principle. Since A is a projection operator, application of the antisymmetrizer to a wave function that is already totally antisymmetric has no effect, acting as the identity operator.