Zirconia-based materials combine good thermomechanical properties and oxygen ion conductivity with chemical inertness and structural stability in a range of chemical environments. Polycrystalline materials, which are used in the bulk of applications, display a rich variety of segregation behaviour due to impurities which are invariably present either in the starting powders or inadvertently incorporated during processing. The mechanisms whereby, many, though not all, of these impurities and alloying components accumulate at the external or grain boundary interfaces are examined. The accumulation of impurities or components at the grain boundary can significantly change the grain boundary composition. Consequently, many of the macroscopic properties of these materials can depend critically on the chemistry of the grain boundary. An overview from both a thermodynamic and atomistic approach, of the development of the grain boundary network and the changing chemistry in the region of the grain boundary during the sintering process is presented. A qualitative appraisal of some current segregation and sintering theories are discussed. Surface analysis, by a variety of techniques, can probe the composition of interfaces within ZrO2-based ceramics giving valuable information of the distribution of impurities and components. A review of the contribution of surface analysis, particularly X-ray photoelectron spectroscopy, to the understanding of segregation phenomena and its effects on ceramic properties, is given. The review concentrates on Y2O3-ZrO2, CeO2-Y2O3-ZrO2 and Al2O3-Y2O3-ZrO2. The contribution of surface analysis to the understanding of low temperature degradation of yttria-tetragonal zirconia polycrystal is also examined.