The light microscope is one of the most important tools used by metallurgists in failure analysis. Development of electron metallographic instruments, such as the scanning electron microscope, has not diminished the importance of light microscopy. Basically, the light microscope is used to define the relationship of the fracture path to microstructural features and to assess the nature of the microstructure and its influence on the failure mechanism. Microscopic examination is used to detect abnormalities due to material quality, fabrication, heat treatment and service conditions. Proper implementation of light microscopy is of critical importance in failure analysis.