Within the emerging field of medicinal inorganic chemistry, the realization that metal complexes can be designed as both therapeutic and diagnostic agents with novel mechanisms of action is increasing. Some recent advances are highlighted in this review, beginning with the success of platinum anticancer complexes and attempts to extend such activity to other transition metals, even to arsenic. Lithium is widely used for bipolar affective disorders, and gold is used for the treatment of rheumatoid arthritis. Metal ions also play crucial roles in contrast agents for magnetic resonance imaging and in radiopharmaceuticals used for imaging and therapy. Metal complexes offer flexible design platforms as enzyme inhibitors, and metals in enzyme active sites can be key drug targets. The antimicrobial and antiviral activities of certain metal complexes may prove useful in the fight against antibiotic resistance. Metals play key roles, too, in the control of small signaling molecules such as nitric oxide and carbon monoxide. Control of the uptake and distribution of the essential metals also presents a challenge, which is aided by modern genomic knowledge.