How is pole placement used to design state feedback controllers?

Pole placement (pole assignment) designs state feedback gain K such that closed-loop poles are at desired locations. With u = -Kx + r, the closed-loop system has poles at eigenvalues of (A - BK). Designer chooses poles based on desired transient response (damping, speed). Ackermann's formula or direct coefficient matching computes K. The system must be controllable. All states must be measured or estimated (using an observer). Pole placement gives complete freedom in pole location unlike classical compensators.