This chapter discusses some important factors involved in the atmospheric corrosion of engineering materials. The discussion begins with a description of elements necessary for the operation of a galvanic corrosion cell and corrosion reactions, followed by the types of atmospheric corrosion attack. Some of the atmospheric parameters and their effects on the corrosion of several metals are then reviewed. The following sections provide information on air chemistry, principal pollutants inducing corrosion, thermodynamics as well as models for prediction of atmospheric corrosion, and use of Pourbaix diagrams. The phenomenon of precipitation runoff on the corroded metal surface is then discussed. The chapter also describes the role of microbes or bacteria in the corrosion of metals. It concludes by providing information on the trends in atmospheric corrosion research and methods.