The thermodynamics and phase transitions in lithium intercalation oxides are discussed. Changes in the host structure can be driven by configurational Li-vacancy interactions, variations in electron count or by changes in the stability of the oxygen packing. The formalism to predict the lithium-vacancy ordered configurations and their free energy is presented and calculations of the phase diagram of Li x CoO 2 in the spinel and layered structure using this formalism are reviewed. Layered Li x CoO 2 has the richest phase diagram with ordering and staging transitions, and changes in host structure at low lithium contents. In general we find relatively low order-disorder transitions due to the strong screening of the lithium-lithium interaction by oxygen. From calculating the energy difference between the spinel and layered structure for several transition metal oxides it is found that a driving force for transition to spinel will always exist when a layered lithium transition metal oxide is delithiated. The limitations of current first principles methods in studying electronic transitions are discussed.