Abstract : This book, written by a group of specialists in the different areas involved, summarises what we understand of the production and distribution of oxygen, the most abundant metal in the Universe. After presenting the methods of oxygen abundance determination in various media, it traces a panorama of oxygen in the Universe, describes the mechanisms and sites of oxygen production and finally discusses the chemical evolution of oxygen in different galactic and extragalactic contexts. An appendix thoroughly discusses the oxygen atomic data. This book is intended for the graduate student as well as for the professional astrophysicist. Its aim is to provide the reader with tools for a deeper understanding of the covered topics rather than just to summarise the latest results. Following the thread of oxygen, the reader can gain a diagonal perspective of the realm of stellar, galactic and extragalactic astronomy.