Ferroelectric materials are nonlinear dielectrics, having a dielectric constant which is a function of the electric field. The nonlinear behavior of these materials makes them candidates for the realization of advanced high frequency devices which can operate up to the millimeter range. Ferroelectrics have been successfully employed in many optical devices, but their application at high frequency has been limited, mostly due to the large bias voltage required to significantly change the electrical properties of the bulk material. However, today there are several new techniques available to produce ferroelectric thin films and thin ceramics which only require low or medium bias voltage. These processes open the way for development of a new family of devices which are fully compatible with conventional analog and digital electronic circuits. Use of tunable dielectric material finds applications in many new devices including tunable phase shifters, tunable filters, and tunable beam scan antennas. High quality thin films and thin ceramics of PbTiO3 (PTO), BaTiO3 (BTO), BaxSr1-xTiO3 (BST), and PbxCa1-xTiO3 (PCT) have been produced and characterized. A 2.5 GHz tunable phase shifter, realized using BTO in microstrip configuration, is proposed and tested.