Zirconium titanate (ZrTiO4) ceramics have been prepared by the mixed oxide route using small additions of ZnO, Y2O3 or CuO Specimens were sintered mainly at 1400 degrees C and cooled at various rates : water-quench, air-quench, 300 degrees C h(-1), 120 degrees C h -1, 6 degrees C h(-1) and 1 degrees C h(-1). Products prepared with additives exhibited densities of at least 93% of the theoretical value. As the cooling rate after sintering was decreased, the length of the lattice parameter in the b direction was reduced and transmission electron diffraction revealed superlattice reflections associated with cation ordering. For specimens cooled at 1 degrees C h(-1), electron diffraction patterns exhibited features consistent with an incommensurate superstructure in the a direction. The dielectric Q value of rapidly cooled (air-quenched) ceramics was 2000 at 5 GHz. With an increase in the degree of cation ordering the Q value increased to a maxim um of 4400 for specimens cooled at 6 degrees C h(-1). For specimens cooled at the slowest rate (1 degrees C h(-1)) the Q value fell to 2000 due in part to the presence of microcracks and exsolved ZrO2. Diffusion of trivalent impurities (yttria) into the host ZrTiO4 grains also led to a lowering of the Q values. The microwave dielectric properties of zirconium titanate ceramics are sensitive to processing conditions and mircrostructural features. The highest Q values (lowest loss) should be achieved in homogeneous specimens, free of trivalent impurities and lattice defects, in which low Q-value second phases, microcracks and pores are eliminated.