This seminar presents an overview of defect based testing. Electrical behavior and circuit effects of CMOS IC defects and failure mechanisms are described, and test methods that can be effective in detecting them are overviewed. Basic fault models that represent those defects are discussed, along with how they can be used in test generation, test evaluation and defect localization. We also address how to apply defect based testing in production, including the use of design-for-test (DFT) features such as serial-scan and BIST.