The metastable-to-equilibrium phase evolution over a wide range of compositions in the TiO2-YO3/2-ZrO2 system was investigated. The competing phases are all derivatives of the fluorite structure and compositions within the fluorite and pyrochlore fields exhibit technologically interesting ionic and mixed ionic-electronic conductivity. Powders of various compositions were synthesized by precursor routes, pyrolyzed and subsequently heat-treated in a stepwise manner at progressively higher temperatures to explore the sequence of phase evolution. Extended solid solutions with amorphous, fluorite and ordered pyrochlore structures were produced over significant composition ranges within the ternary. The study also sheds new light on the correct form of the phase equilibria at 1300°C.