This review provides an overview of the complex mechanisms plants use to control auxin levels, the movement of auxin through the plant, and the emerging understanding of auxin signaling. Auxin, primarily indole-3-acetic acid (IAA), is a critical hormone for plant growth and development. IAA can be synthesized from tryptophan (Trp) through various pathways, including Trp-dependent and Trp-independent routes. The biosynthesis of IAA involves multiple enzymes and pathways, with the exact mechanisms still not fully elucidated. IAA can also be obtained from β-oxidation of indole-3-butyric acid (IBA) or by hydrolysis of IAA conjugates. Plants can inactivate IAA through oxidation or formation of non-hydrolysable conjugates. Auxin signaling is mediated by the SCF(TIR1) E3 ubiquitin ligase complex, which regulates gene expression by altering Aux/IAA repressor degradation. The review also discusses the interaction between auxin and other phytohormones, highlighting the importance of auxin in plant growth and development. Despite significant progress, many fundamental questions and details remain unresolved in the field of auxin research.This review provides an overview of the complex mechanisms plants use to control auxin levels, the movement of auxin through the plant, and the emerging understanding of auxin signaling. Auxin, primarily indole-3-acetic acid (IAA), is a critical hormone for plant growth and development. IAA can be synthesized from tryptophan (Trp) through various pathways, including Trp-dependent and Trp-independent routes. The biosynthesis of IAA involves multiple enzymes and pathways, with the exact mechanisms still not fully elucidated. IAA can also be obtained from β-oxidation of indole-3-butyric acid (IBA) or by hydrolysis of IAA conjugates. Plants can inactivate IAA through oxidation or formation of non-hydrolysable conjugates. Auxin signaling is mediated by the SCF(TIR1) E3 ubiquitin ligase complex, which regulates gene expression by altering Aux/IAA repressor degradation. The review also discusses the interaction between auxin and other phytohormones, highlighting the importance of auxin in plant growth and development. Despite significant progress, many fundamental questions and details remain unresolved in the field of auxin research.