Physical and chemical processes that operate at low temperature in Earth’s surface environments and in other planetary settings have left an indelible record of the evolution and interactions of planetary surface and near-surface reservoirs. This chapter reviews the chemistry of oxygen (elemental andisotopic) inlunar, planetary, and Earth surface reservoirs. The discussion begins with a brief review of the relative abundances of oxygen isotopes in planetary materials, including lunar samples, the SNC (Martian) meteorites, and components that are inferred to come from Martian surface pools. This is followed by a brief, largely historical account of the development of oxygen isotope geochemistry in Earth-surface materials. The discussion then transitions, using an Earth systems perspective, into an overview of developments in oxygen isotope geochemistry of atmospheric compounds. This treatment includes recent studies that (1) use high-precision measurements of δ17O and δ18O to characterize atmospheric oxygen; (2) apply information about isotopically substituted species (isotopologs) for characterizing the position-dependent isotopic fractionations of some oxygen-bearing atmospheric species; and (3) investigate non mass-dependent isotopic fractionations in ozone and other atmospheric species. The discussion then examines the evidence and models that point to change in the oxygen cycle and oxidation chemistry in Earth surface environments over the course of geologic time. We use the subdivisions of the Earth systems - the hydrosphere, geosphere and biosphere, as a basis for examining these changes. This record is explored in the context of hypotheses and data that relate to the nature of the changes and transformations in the oxidation state of these different components of the Earth’s surface environments. We conclude with a brief accounting of areas of research where scientific inquiry is presently very active.