The second edition of Metal Ions in Biochemistry deals with the multidisciplinary subject of bio-inorganic chemistry, encompassing the disciplines of inorganic chemistry, biochemistry and medicine. The book deals with the role of metal ions in biochemistry, emphasising that biochemistry is mainly the chemistry of metal-biochemical complexes. Hence, the book starts with the structures of biochemicals and the identification of their metal binding sites. Thermodynamic and kinetic properties of the complexes are explained from the point of view of the nature of metal-ligand bonds. Various catalytic and structural roles of metal ions in biochemicals are discussed in detail. Features The role of Na+ and K+ in brain chemistry. The role of zinc insulin in glucose metabolism and its enhancement by vanadium and chromium compounds. Discussion of the role of zinc signals, zinc fingers and cascade effect in biochemistry. Haemoglobin synthesis and the role of vitamin B12 in it. The role of lanthanides in biochemical systems. A detailed discussion of the role of non-metals in biochemistry, a topic missing in most of the books on bio-inorganic chemistry. The study of bio-inorganic chemistry makes biochemists rethink the mechanistic pathways of biochemical reactions mediated by metal ions. There is a realisation of the role of metal complexes and inorganic ions as therapeutics such as iron in leukaemia, thalassemia and sickle cell anaemia, iodine in hypothyroidism and zinc, vanadium and chromium in glucose metabolism. The most recent realisation is of the use of zinc in the prevention and treatment of COVID-19.