Seawater is a hostile environment not only for people but also for metals and alloys. It is often considered that sea water is the most severe environment to which materials can be exposed. Warmer water accelerates the rate of corrosion due to high temperature and particularly aggressive. In this chapter, marine corrosion, its mechanism, factors affecting corrosion and several methods adopted for the prevention of corrosion are described with an emphasis on marine corrosion inhibitors. Organic compounds containing hetero atoms like O, N, S, etc., along with double and triple bonds are found to be very effective in preventing marine corrosion of alloys and metals. Most of the corrosion inhibitors are found to show inhibition property by getting adsorbed on to the metal surface through the principle of different adsorption isotherms known. The maximum corrosion inhibition efficiency of organic inhibitors is found to be more than 99%. The use of inorganic compounds and paints as corrosion inhibitors is discussed.