Molybdate-based corrosion inhibitors have been used in cooling water treatment for some time. Their widespread use has been limited, however, by key technical and economic factors. This paper explores a number of new products, recently developed, which demonstrate why molybdate-based programs can now be used in almost any application. An in-depth technical discussion on how molybdates function as inhibitors and what other treatments aid or hinder their effectiveness is included. Laboratory data is presented to verify the theoretical. Case histories of actual cooling water applications are discussed which show when and where molybdate-based products have outperformed other, more traditional treatments. Economics are also included which outline the relative costs of these programs versus other treatment programs. Finally, the environmental aspects of molybdate are also outlined in the paper. With metallic treatments such as zinc and chromate under close scrutiny by governmental agencies, the existing laws governing the discharge of molybdate are reviewed and the future disposition of this material scrutinized.