This thesis discusses the matrix representations of various complex stability regions and the designs of fixed-order controllers using positive polynomials. Stability regions presented in this thesis include one dimensional, two dimensional and their combinations. Regions such as shifted half plane, circle, ellipse, parabola, and union of regions are narrated and collated. A stabilizing control problem with low-order controller to satisfy additional constraints on the closed-loop pole location is explored in the thesis. A H-infinity control problem using positive polynomial concepts is also investigated. The longitudinal auto-pilot designs for a low-speed uninhabited experimental aircraft are presented to illustrate the fixed-order controller design using positive polynomials.