The Imperial House of Japan (皇室, kōshitsu^?), also referred to as the Imperial Family, comprises those members of the extended family of the reigning Emperor of Japan who undertake official and public duties. Under the present Constitution of Japan, the emperor is the symbol of the state and unity of the people. Other members of the imperial family perform ceremonial and social duties, but have no role in the affairs of government. The duties as an emperor are passed down the line to children and their children's children and so on.

The Japanese monarchy is the oldest continuous hereditary monarchy in the world. The imperial house recognizes 125 monarchs beginning with the legendary Emperor Jimmu (traditionally dated to February 11, 660 BC) and continuing up to the current emperor, Akihito; see its family tree. However, there is no historical evidence for the genealogical relationships, and in most cases even the existence of, the first 25 emperors.

Article 5 of the Imperial Household Law (皇室典範, Kōshitsu Tempan^?) defines the imperial family (皇族^?) as: the empress (皇后, kōgō^?); the empress dowager (皇太后, kōtaigō^?); the grand empress dowager (太皇太后, tai-kōtaigō^?); Emperor's legitimate sons and legitimate grandsons in the legitimate male-line (親王, shinnō^?) and their consorts (親王妃, shinnōhi^?); Emperor's unmarried legitimate daughters and unmarried legitimate granddaughters in the legitimate male-line (内親王, naishinnō^?); Emperor's other male decendants in the legitimate male-line (王, ō^?) and their their consorts (王妃, ōhi^?); and the Emperor's other unmarried female decendants in the legitimate male-line (女王, Joō^?). In English, shinnō and ō are both translated as "princes" as well as naishinnō, shinnōhi, ōhi and Joō as "princesses".

Japan ⁱ/dʒəˈpæn/ (Japanese: 日本 Nihon or Nippon; formally 日本国  Nippon-koku or Nihon-koku, literally the State of Japan) is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south. The characters that make up Japan's name mean "sun-origin", which is why Japan is sometimes referred to as the "Land of the Rising Sun".

Japan is an archipelago of 6,852 islands. The four largest islands are Honshū, Hokkaidō, Kyūshū and Shikoku, together accounting for ninety-seven percent of Japan's land area. Japan has the world's tenth-largest population, with over 127 million people. The Greater Tokyo Area, which includes the de facto capital city of Tokyo and several surrounding prefectures, is the largest metropolitan area in the world, with over 30 million residents.

Archaeological research indicates that people lived in Japan as early as the Upper Paleolithic period. The first written mention of Japan is in Chinese history texts from the 1st century AD. Influence from other nations followed by long periods of isolation has characterized Japan's history. In the late 19th and early 20th centuries, victory in the First Sino-Japanese War, the Russo-Japanese War and World War I allowed Japan to expand its empire during a period of increasing militarism. The Second Sino-Japanese War of 1937 expanded into part of World War II in 1941, which came to an end in 1945 following the atomic bombings of Hiroshima and Nagasaki. Since adopting its revised constitution in 1947, Japan has maintained a unitary constitutional monarchy with an emperor and an elected parliament called the Diet.

A royal house or royal dynasty consists of at least one, but usually more monarchs who are related to one another, as well as their non-reigning descendants and spouses. Monarchs of the same realm who are not related to one another are usually deemed to belong to different houses, and each house is designated by a name which distinguishes it from other houses. Strictly, a "royal house" is a dynasty whose members reign while bearing the title of king or queen, although it has become common to refer to any family which legally exercises sovereignty by hereditary right as a royal family, and its members as "royalty" or (colloquially) "royals". Historically, ruling families often consist of a senior and several junior branches, which are akin, but may have diverged in descent from a common ancestor many generations ago. The name used to refer to a royal house may or may not also be used by its members as a surname. Rather, members of dynasties are usually referred to by their titles, which may or may not also be hereditary.

Crown Princess Masako (皇太子徳仁親王妃雅子, Kōtaishi Naruhito Shinnōhi Masako^?), formerly Masako Owada (小和田雅子, Owada Masako^?, born 9 December 1963) is the wife of Crown Prince Naruhito, the first son of the Emperor Akihito and the Empress Michiko, and a member of the Imperial House of Japan through marriage.

Born in Tokyo, Japan, she was originally named Masako Owada (小和田 雅子, Owada Masako^?). She is eldest daughter of Hisashi Owada, a senior diplomat, and President of the International Court of Justice. She has two younger sisters, twins named Setsuko and Reiko.

Masako went to live in Moscow with her parents when she was two years old, where she completed her kindergarten education. Upon returning to Japan, she attended a private girls' school in Tokyo, Denenchofu Futaba, from elementary school through her second year of senior high school. Masako and her family moved to the United States, and settled in a suburb of Boston, Massachusetts called Belmont, when her father became a guest professor at Harvard University and vice ambassador to the United States. In 1981, she graduated from Belmont High School, the public high school of the community where she was president of the National Honor Society, and she entered Radcliffe College.