The Emperor of Japan is the monarch and the head of the Imperial Family of Japan. Under the Constitution of Japan, he is defined as the symbol of the Japanese state and the unity of the Japanese people, and his position is derived from "the will of the people with whom resides sovereign power". Imperial Household Law governs the line of imperial succession. The emperor is immune from prosecution by the Supreme Court of Japan. He is also the head of the Shinto religion. In Japanese, the emperor is called Tennō (天皇, pronounced [tennoꜜː]), literally "Emperor of heaven" or "Heavenly Sovereign". The Japanese Shinto religion holds him to be the direct descendant of the sun goddess Amaterasu. The emperor is also the head of all national Japanese orders, decorations, medals, and awards. In English, the use of the term Mikado (帝／御門) for the emperor was once common but is now considered obsolete.

The Imperial House of Japan, known by their name the Yamato Dynasty, is amongst the oldest in the world, with its historical origins in the late Kofun period of the 3rd–6th centuries AD. According to the mythological accounts of the Kojiki and Nihon Shoki, Japan was founded in 660 BC by Emperor Jimmu.

The role of the emperor of Japan has historically alternated between a largely ceremonial symbolic role and that of an actual imperial ruler. Since the establishment of the first shogunate in 1192, the emperors of Japan have rarely taken on a role as supreme battlefield commander, unlike many Western monarchs. Japanese emperors have nearly always been controlled by external political forces, to varying degrees. For example, between 1192 and 1867, the shōguns, or their shikken regents in Kamakura (1203–1333), were the de facto rulers of Japan, although they were nominally appointed by the emperor. After the Meiji Restoration in 1867, the emperor was the embodiment of all sovereign power in the realm, as enshrined in the Meiji Constitution of 1889. Since the enactment of the 1947 constitution, the role of emperor has been relegated to that of a ceremonial head of state without even nominal political powers.

Since the mid-nineteenth century, the Imperial Palace has been called Kyūjō (宮城), later Kōkyo (皇居), and is located on the former site of Edo Castle in the heart of Tokyo (the current capital of Japan). Earlier, emperors resided in Kyoto (the ancient capital) for nearly eleven centuries. The Emperor's Birthday (currently 23 February) is a national holiday.

Naruhito is the current emperor of Japan. He acceded to the Chrysanthemum Throne upon the abdication of his father, Emperor Akihito, on 1 May 2019.