The Nyquist stability criterion evaluates the closed-loop stability of a feedback control system directly from its open-loop frequency response without requiring explicit calculation of closed-loop poles. By mapping the Bromwich contour from the complex s-plane into the G(s)H(s) plane, the criterion employs Cauchy's argument principle: the number of unstable closed-loop poles Z equals the number of unstable open-loop poles P plus the net number of clockwise encirclements N of the critical point (-1, j0).