Auxins are a phytohormones that regulates of processes related to plant growth and morphogenesis, therefore their deficiency or excess results in severe developmental disorders. Plants have developed mechanisms aimed at regulating the level of the active form of these hormones, including their: directional transport, local biosynthesis, and degradation, as well as reversible and irreversible inactivation by binding to additional chemical groups. Despite almost a hundred years since the discovery of auxins, the functioning of these mechanisms, especially at the level of metabolism, is still not fully understood. In recent years, thanks to the development of new research methods, significant progress has been made in this field. This applies to both the identification of auxin biosynthetic pathways and the genes involved in them, as well as the detection of new auxin metabolites, their mutual connections and enzymes involved in their biosynthesis, transformation, and degradation. This work focuses on summarizing the current knowledge on this topic, considering the relationship of auxin metabolism with developmental processes and the response to changing environmental conditions.