Isatin, 1H-indole-2,3-dione, is a heterocyclic compound of significant importance in medicinal chemistry. It is a synthetically versatile molecule, a precursor for a large number of pharmacologically active compounds. Isatin and its derivatives have aroused great attention in recent years due to their wide variety of biological activities, relevant to application as insecticides and fungicides and in a broad range of drug therapies, including anticancer drugs, antibiotics and antidepressants. The purpose of this review is to provide an overview of the pharmacological activities of isatin and its synthetic and natural derivatives. Molecular modifications to tailor the properties of isatin and its derivatives are also discussed.