Available information on atmospheric corrosion over long periods of time (10–20 years or longer) is unfortunately very scanty despite its great usefulness; in fact, only from such type of data can reliable long-term atmospheric corrosion predictions be made. This paper reports the results obtained after 13–16 years of field exposure tests at various Spanish test sites including several types of atmosphere: rural (El Escorial), urban (Madrid, Zaragoza), industrial (Bilbao), and marine (Barcelona, Cadiz, Cabo Negro, Alicante). Panels of low-carbon steel, zinc, copper, and aluminum were removed from open-air racks after 1–6, 8, 10, 13, and 16 years of exposure, and their weight losses used to determine the corrosion rate. Long-term corrosion data were found to conform to a general equation, C = Atn, where A and C are the corrosion losses after one and t years of exposure, respectively, and n is a constant. Only mild steel in scarcely aggressive atmospheres of central Spain was found to fit a more complex equation. The results are compared with those found throughout the world, which were compiled in a comprehensive literature survey. Finally, an attempt was made at correlating exponent n with the type of atmosphere for each metal studied.