Metals, primarily affected building materials by corrosion, are frequently used in façade and roof coverings, structural system, ornaments, door and window frames, as reinforcing steel in concrete and etc. Therefore, it is critical to prevent corrosion and to understand its mechanism. Moreover, corrosion prove important especially for the building envelope because it is susceptible to atmospheric conditions which lead to building material damages in time. Since corrosion develops slowly, its effects on building materials are usually ignored. However, it can be prevented during the architectural design phase by choosing and applying appropriate materials and detail designs while taking into account environmental conditions. Also, studies show that corrosion can cause devastating damage to metals, and it is inevitable in the long term especially for reinforced concrete systems if periodic maintenance and repair are not carried out. In this study, corrosion mechanism and corrosion types are explained in detail, and lastly, protection methods against corrosion are discussed.