We emphasize failure mechanism issues which range from practical aspects to basic failure mechanisms. The course will teach the student the understanding of why failure occurs at the device level. Failure can occur in compound semiconductor devices at surfaces and interfaces, in the substrate, at Schottky barriers, at ohmic contacts, by electromigration and by corrosion of the metallizations. Optoelectronic devices share some of these failure mechanisms with electronic devices and these will be presented as part of the course. Other increasingly important failure mechanisms such as radiation effects, electrostatic discharge, high current and high power effects are included within the scope of this course.