Undoped zirconia has low ionic conductivity which is not sufficient for the practical application. Addition of dopants improve the ionic conductivity by stabilization of zirconia in the cubic phase which is most widely used for practical applications such as solid electrolyte in oxygen sensors and solid oxide fuel cells. The structural and ionic conductivity of zirconia doped with calcia, gadolinia or ceria is widely studied while there is lack in the literature concerning studying of the structural and ionic conductivity of scandia stabilized zirconia system co-doped with calcia, gadolinia or ceria and zirconia co-doped with calcia and gadolinia or with calcia and ceria. This book provide improving the ionic conductivity of zirconia and also provide an attempt to obtain new zirconia-based oxide electrolytes by studying the structural and electrical properties of co-doped zirconia based on single doped zirconia system which is widely studied. The structural and electrical properties of stabilized zirconia investigation will help students or the professionals who considering zirconia based electrolytes for Solid Oxide Fuel Cells or Oxygen Sensors.