The article focuses on the Imperial institution in Japan. After an overview on the role played by Emperors until the mid-XIX century, the article examines the influence of the German theories on sovereignty during the drafting procedure of the 1889 Constitution. Here the Emperor was qualified as a living god and the only source of all the sovereignty. After the defeat in WWII and the US occupation, the 1946 Constitution modified the sovreignty principle and shaped a human Emperor, with just a symbolic role.