Koreans in Japan are the ethnic Korean residents of Japan. They currently constitute the second largest ethnic group in Japan. The majority of Koreans in Japan are Zainichi Koreans, often known simply as Zainichi (在日, lit. "foreign citizen residing in Japan"), who are the permanent ethnic Korean residents of Japan. The term "Zainichi Korean" refers only to long-term Korean residents of Japan who trace their roots to Korea under Japanese rule, distinguishing them from the later wave of Korean migrants who came mostly in the 1980s, and from pre-modern immigrants dating back to antiquity.

The Japanese word "Zainichi" itself means a foreign citizen "staying in Japan" and implies temporary residence. Nevertheless, the term "Zainichi Korean" is used to describe settled permanent residents of Japan, both those who have retained either their Joseon or South Korean / North Korean nationalities, and even sometimes, but not always, includes Japanese citizens of Korean descent who acquired Japanese nationality by naturalization or by birth from one or both parents who have Japanese citizenship.