Nondestructive testing, also known as nondestructive evaluation, nondestructive inspection, and sometimes as condition or health-based monitoring, is a wide field of testing procedures that do not damage or destroy the interrogated object. Many different NDT techniques exist, such as ultrasonics, acoustic emission, or magnetic flux leakage, but essentially NDT can be summed up as analysis of energy propagation: the presence of a flaw or anomaly will change the energy's characteristics, which is reported by the NDT technique as a signal from a flaw. This category is devoted to NDT, its techniques and analysis and companies offering NDT products and services.