Hexon is one of the major structural components of the capsid, an icosahedral structure that envelops and protects the genetic material of adenoviruses. There are 240 hexon capsomeres per capsid and each capsomere is made out of a homotrimer of the hexon protein (> 900 residues). Human adenovirus are recognised as being an important cause of respiratory illnesses, conjunctivitis, gastroenteritis and, more recently, as a potential cause of sexually transmitted diseases. Adenovirus vectors, particularly those based on Ad5, have shown potential for the development of gene therapy protocols and clinical use.