Maraging steels comprise a special class of high-strength steels that differ from conventional steels in that they are hardened by a metallurgical reaction that does not involve carbon. Instead, these steels are strengthened by the precipitation of intermetallic compounds at temperatures of about 480 deg C. Commercial maraging steels are designed to provide specific levels of yield strength in the range of 1030 to 2420 MPa. However, some experimental maraging steels have yield strengths as high as 3450 MPa. These steels typically have very high nickel, cobalt, and molybdenum contents and very low carbon contents. This article outlines the processing of maraging steels: melting, hot working, cold working, machining, heat treating, surface treatment, and welding. It also covers mechanical and physical properties as well as tooling and aerospace applications, where maraging steels are extensively used.