The Ph. D thesis of Sanjeeb Kumar Rout entitled "Phase Formation and Dielectric Studies of Some BaO-TiO2-ZrO2 Based Perovskite Systems" submitted to the National Institute of Technology (NIT), Rourkela, Orissa, India in the year 2006. The thesis was submitted to NIT Rourkela under the joint supervision of Prof. S. Panigrahi, Dept of Physics and Prof. J.Bera, Dept of Ceramic Engineering of the same Institute. The thesis was examined and well appreciated by Prof. E. V. Cola, USA and Prof T. P. Sinha, India. The thesis presents a detailed phase formation, structural, micro-structural and dielectric studies of some BaO-TiO2-ZrO2 based perovskite systems. The special attention has been paid towards the relaxor behavior of some composition in the system. The author has made an attempt to shift the phase transition temperature of the observed relaxor towards the room temperature.