Nisei is a Japanese-language term used in countries in North America and South America to specify the ethnically Japanese children born in the new country to Japanese-born immigrants. The Nisei are considered the second generation and the grandchildren of the Japanese-born immigrants are called Sansei, or third generation. Though nisei means "second-generation immigrant", it often refers to the children of the initial diaspora, occurring in the late 19th and early 20th centuries, and overlapping with the G.I. and silent generations.

The Japanese diaspora and its individual members, known as Nikkei (日系) or as Nikkeijin (日系人), comprise the Japanese emigrants from Japan residing in a country outside Japan. Emigration from Japan was recorded as early as the 15th century to the Philippines, but did not become a mass phenomenon until the Meiji period (1868–1912), when Japanese emigrated to the Philippines and to the Americas. There was significant emigration to the territories of the Empire of Japan during the period of Japanese colonial expansion (1875–1945); however, most of these emigrants repatriated to Japan after the 1945 surrender of Japan ended World War II in Asia.