Eddy current testing is a key technology among electromagnetic non-destructive testings at present and this situation was motivated by a stringent need to detect small cracks in tubing of a steam generator of nuclear power plants. In these five years the ECT technology has been enhanced very much, demonstrating that high performanced sensors for ECT are now ready to be applied to the annual inspection of steam generator tubing with use of arrayed micro sensors for ECT. In addition to the innovative technology, an inversion technique is being theoretically developed to make reconstruction of defects possible with use of data from the arrayed sensors. Rapid growth of interest in electromagnetic nondestructive evaluation have brought together experts from different parts of the world, as reflected in this work. The book is intended for engineers, researchers and practitioners working in the area of electromagnetism.