Given that the full internal state vector is available, this information can be fed back and used for the design of a static state feedback controller. The chapter presents the classical approach of prescribing desired poles for the closed-loop system and demonstrates that the steady-state error can be removed by combining the state feedback controller with an integrator. For MIMO systems, the state feedback gain matrix for the controller is not unique. The multi-input problem can be reduced to a single-input problem by means of the cyclic design method. In general, not all components of the state vector are directly measurable. In this case, the not fully known state vector can be estimated by means of an observer and the vector of state estimates be used as a substitute in a standard state feedback control design. The behaviour of a closed-loop state feedback system making use of an observer is close to the one of a state feedback control in which all states are measurable. It is computationally not efficient to estimate internal states that can be directly measured. The unnecessary computational effort can be avoided by means of a reduced order observer that uses some or all measured states for the computation of the missing ones. This chapter addresses only the full order observer and refers to the literature for the development of a reduced order observer. A theoretical and practically important result is that the observer dynamics can be designed independently from the state feedback dynamics which is known as the separation principle.