Metal ions are fundamental to bioinorganic chemistry, playing essential roles in catalyzing biochemical reactions and maintaining metal homeostasis. They are indispensable for sustaining biological processes on Earth. Over the years, researchers have developed a range of scientific tools—including synthetic inorganic chemistry, spectroscopy, structural biology, protein engineering, and computational modeling—to investigate the functions of metals in biological systems. As research advances, new insights continue to emerge, deepening our understanding of the diverse roles and mechanisms of metal ions in life.