Hormones are a class of molecules, which mediate their effects by regulating a variety of signalling pathways. Melatonin (N-acetyl-5-methoxytryptamine), a pineal gland hormone, is one among the categories of compounds having various therapeutic and pharmacological effects. Melatonin has many intracellular as well as extracellular targets including apoptosis, metastasis, angiogenesis and inflammatory pathways. Gene-profile studies have further established its antagonist effect on the various genes involved in the tumour progression, neurodegeneration and ageing. It has also been known to reduce the toxicity induced by chemotherapeutic agents in advanced stages of tumour. The present review extensively describes the molecular interactions of melatonin with various recognized cellular targets, which may lead the scientific community to propose novel therapeutic strategies.