Heterocycles are ‘cyclic compounds having as ring members atoms of at least two different elements’. Heterocyclic compounds constitute more than half of all known organic compounds, are prevalent in drug molecules and are a favourite of medicinal chemists. By the end of this course you will be able to name the common monocyclic and bicyclic heterocycles and be able to understand the nomenclature of more complex heterocycles. Unambiguous naming of the novel heterocycles we make as medicinal chemists is essential to protect our inventions in a patent.