This article provides an overview of the degradation of metals and alloys in aqueous systems. The importance of the hydrogen ion lies in its ability to interact with an alloy surface. The article describes the effects of various conditions of pH on corrosion including strongly acid conditions, near-neutral conditions, and strongly basic conditions as well as the effects of temperature on corrosion. The influence of the fluid flow rate on corrosion depends on the alloy, fluid components, fluid physical properties, geometry in which the fluid is contained, and corrosion mechanism. The article discusses the influence of fluid flow rate through specific examples. It concludes with information on how the concentration of dissolved species works with other variables to influence corrosion behavior.