The advantages and limitations of aluminum metallization are reviewed and compared with other systems used for integrated circuits. Metallization system properties of particular importance are summarized, including initial physical and chemical properties of the system which define potential performance and reliability considerations. The special requirements for MOS arrays and for multilevel-metallized integrated circuits are described. Recently available knowledge of aluminum metallization process technology and of metallization-related failure mechanisms is reviewed, and new results of experimental studies are presented. It is concluded that aluminum will continue to be the most widely used metallization material, not only for single-level metallized integrated circuits, but also for multilevel LSI arrays.