Active thermography, using electromagnetic excitation, allows detecting defects like cracks which distort the flow of current in the component under examination. Like other thermography techniques it is rapid and reliably 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 paper, the specific advantages of both coupling methods are discussed, including the efficiency of the coupling and optimization strategies for testing and also the necessary algorithms required to analyze the data. Taking these considerations into account a number of different systems for laboratory and practical application were developed.