Single‐ion magnets (SIMs), exhibiting slow magnetization relaxation in the absence of the magnetic field, originate from their single spin‐carrier centre. In pursuit of high‐performance magnetic properties, such as high spin‐reversal barrier and high blocking temperature, various metal centres were investigated to establish SIMs, including 3d and 5d transition metal ions, 4f lanthanide ions, and 5f actinide ions, which possess unique zero‐field splitting and magnetic properties. Therefore, proper ligand field is of great importance to different types of metals. In the given great breakthroughs since the first SIM, Pc2Tb− (Pc=dianion of phthalocyanine), was reported, strategies of ligand field design have emerged. In this review, the developments of SIMs with different metal centres are summarized, as well as the possible strategies. How molecular magnetism works: A summary of single‐ion magnets (SIMs) including the development of 3d, 5d, 4f, and 5f metal‐based SIMs and the possible ligand field strategies for high‐performance SIMs constructions.