Mutation is the process leading to heritable changes in DNA caused mainly by internal and external factors. Recently, studies on mutagenic agents have been increased due to increasing in mutation-related disease. The antimutagenic effect is desired to prevent mutation on genes or to inactivate the mutagenic agent. It seems that the interest in antimutagenic substances displaying multiple mechanisms of action will be an important trend in the research and development of new antimutagenic compounds in the near future. Therefore, this chapter displays various possible mechanisms of action for antimutagenic agent and introduces different types of antimutagens, natural and synthetic, that are considered very important.