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The article discusses the overall building of oxygen in galaxies over the ages as part of the aspect in the chemical evolution of galaxies. It defines chemical evolution as a study of the transformation of gas stars and the resulting evolution of the chemical composition of a galaxy. This galaxy for chemical evolution process offers a useful framework where one can interpret the body of observational data on elemental and isotopic abundances in stars of various ages.

The article presents the Sun as the benchmark for stellar structure and evolution theory where a validation of its theoretical model is crucial for an accurate description of the internal structure and evolution of other stars. It cites a new solar metallicity where oxygen contributes to 43% showing that the Sun is in agreement with surrounding insterstellar medium and nearby B-stars. It notes the use of 3D models as a step towards a more realistic description of the solar photospheric layers.

In this chapter, we first introduce the nuclear processes by which oxygen isotopes can be synthesised and destroyed. We then describe the main astrophysical sites where these reactions may occur, with special emphasis on massive stars and low/intermediate mass stars. [ABSTRACT FROM AUTHOR]

The article discusses ways to determine the abundance of oxygen in different regions of the Universe by first presenting different scales and notation used for said purpose. It notes that each field of astronomy has its own metrics like abundance, when applied to an element like oxygen, usually refers to the ratio of its number density to that of hydrogen. It cites the use of a scale in cool star atmospheres as abundances are determined in relation to reference value and not in absolute value.

A foreword to "Oxygen in the Universe," is presented.