Metallic defects are a significant source of CMOS chip degradation, resulting in yield loss, performance degradation, and reliability risks. Metallic defects cause a spectrum of CMOS problems, including physical defects such as wafer haze, stacking faults, etc. Metal contamination can degrade dielectrics through many mechanisms, including mobile ions, traps, leakage, etc. Diode junctions can be degraded by generation and lifetime degradation, breakdown reduction, etc. CMOS transistors can be degraded through multiple mechanisms, including threshold voltage shifts, threshold hysteresis, mobility reduction, etc. This chapter discusses common sources of metal contamination, the electrical activity of metal contamination, important related metal properties, and the worst metal contaminants. Metal contaminant case studies of DRAM and CMOS imagers are covered.