Iodine is a chemical element with atomic number 53 and one of the most valuable natural resources among the halogen elements. One third of all iodine in the world is produced in Japan. Japan has been regarded as an iodine-sufficient or even excessive country because Japanese has been consuming traditionally large amounts of iodine largely through the intake of seaweed. However, there is no national data on iodine nutrition and its relation to diseases. In this review, a variety of aspects of iodine and also iodine status in Japan is discussed.