The knowledge of insulation ageing is necessary to determine how long the electrical equipment can function. Ageing is a reflection of the chemical and physical changes, in electrical materials or electrical systems, resulting from stresses with the passage of time. The effects of ageing, the reasons why most industries are interested in ageing, the challenges faced by the determination of reliability, the stresses experienced by electrical systems, the problems with ageing diagnostics of large systems, and the considerations to resolve the enigma of electrical ageing are presented.