This lesson is Part 2 of a series on the postulates of quantum mechanics for undergraduate physical chemistry. This lesson introduces the concept of operators. It covers linear operators, eigenfunctions and eigenvalues, Hermitian operators, and Dirac Bracket notation. It is intended to follow an introduction to the first postulate of quantum mechanics (existence of a wavefunction) and the Born intepretation of the wavefunction. This lesson prepares the students for the rest of the postulates.