A systematic design procedure using state-feedback Certainty Equivalence Adaptive Control (CEAC) technique is developed for linear plants and a class of nonlinear plants with unmatched uncertainty. It is shown that a reduced order observer and adaptive laws with normalization in conjunction with the CEAC law result in a stable overall system in the case of linear plants of any relative degree, and a class of nonlinear plants of relative degree two. In the case of higher relative degrees a CEAC approach based on multiple observers is proposed. The proposed schemes guarantee overall system stability and asymptotic tracking.