Maintenance to ensure the integrity of structures is one of the most important issues in modern industry, but more so in the nuclear power industry. This is primarily because complete prevention of all degradation of industrial materials is not possible, at least not in a realistic way. Consequently it is extremely important to detect degradation before machines start to loose their ability to function which may lead to harmful failures. Usually there is some kind of significant interval between the start of material degradation and failure; in other words, degradation usually progresses slowly with time. The problem is whether we can detect precursors of failure in the interval or not. If it is possible, we can have economic as well as safety related benefits because we are able to stop the machine before a functional failure and prevent an accident initiated by the failure of the machine. The benefits are not restricted to the nuclear power industry because it can be applied to any other heavy industry. There are many reasons why many conferences, such as ENDE, have been established to discuss and promote the progress of nondestructive inspection techniques. Whereas nondestructive inspection plays an important role in maintaining structural integrity and the performance of nondestructive inspection techniques should be enhanced in that sense, we need to regard it as one of several components composing “maintenance engineering.” Moreover, although nondestructive inspection is a proactive measure of maintenance, it is not a predictive tool. In fact, it is effective for detecting existing defects and does not say anything about the temporal evolution of defects. On the other hand, a condition monitoring system can offer significantly more useful information as mentioned above. In this paper I would like to introduce the concept of maintenology as a new science and technology in contrast to conventional maintenance engineering and to present several important results on electromagnetic maintenance for nuclear power plants as condition monitoring techniques (CMT). In particular, the introduction of electromagnetic maintenance is expected to play a very promising role in abnormality predictions of many dynamic machines that are required to be inspected regularly by law. Application of the technique would change conventional wisdom in thinking that machines should be taken apart and inspected regularly based on regulations. In many cases, this TBM (time based maintenance) is not too conservative in achieving an optimal maintenance approach.