This article reviews the investigations undertaken into platinum(IV) antitumour compounds since Barnett Rosenberg first noted the activity of platinum(IV) complexes. The chemical and pharmacological properties of the drugs are discussed and both the reactions with individual biomolecules, which have received attention and the characterisation of biotransformation products from animal and clinical trials are reviewed. The bioinorganic chemistry of platinum(IV) complexes has not previously been reviewed, and the purpose here is to provide insight into the requirements for the antitumour activity of platinum(IV) complexes.