Active thermography, using electromagnetic excitation, is a non-contacting, non-destructive evaluation method with a wide range of applications. It allows detecting inhomogenities, like cracks, at or close to the surface of metallic components fast and reliable utilizing infrared imaging. Electric current can be used in two ways for thermography: In induction thermography a current is coupled to the component by passing an AC current through a coil which is in close proximity to the component inspected, while in conduction thermography the current is coupled directly into the component. In this presentationm, we present the basics of this NDE method, along with several component examples and how to build systems for the inspection. The detectability of cracks with high and low residual stresses will be discussed and compared to other surface testing methods as well as the reliability of the method and the prospects for automation. In addition this paper shows first results on high and low conductive materials.