The reliability of an electrical power system depends on the performance and availability of its components, such as power transformers. Due to the increasing age of the transformer population, condition assessment and thus onsite diagnostics are important issues to secure the reliable operation of electrical power systems. During the last decades, major works have been being carried out for the development of reliable and accurate condition assessment techniques. The applicability of the different condition assessment techniques are discussed in the special issue from “Energies” journal on “Power Transformer Condition Assessment” . Complete issue can be accessed from the link below.