The main requirement for defect detection using microwaves is that the material under test is fairly non-conductive, in order for the microwaves to be able to propagate through the material. There must also be a detectable contrast between the defect and the surrounding material, i.e. a difference in density, chemical composition, or moisture content. The SATIMO Quality Control System can be used for a wide range of products. This chapter shows a couple of practical implementations.