By or BY may refer to:
The Byzantine Empire, also referred to as the Eastern Roman Empire, was the continuation of the Roman Empire in the East during Late Antiquity and the Middle Ages, when its capital city was Constantinople (modern-day Istanbul, which had been founded as Byzantium).
The bystander effect, or bystander apathy, is a social psychological phenomenon in which individuals are less likely to offer help to a victim when other people are present.
The BYU Cougars football team is the college football program representing Brigham Young University (BYU), a private university owned by The Church of Jesus Christ of Latter-day Saints (LDS Church) and located in Provo, Utah.
The Byelorussian Soviet Socialist Republic (BSSR, or Byelorussian SSR; Belarusian: Bielaruskaja Savieckaja Sacyjalistyčnaja Respublika or Bielaruskaja SSR, Russian: Belorusskaya Sovetskaya Sotsialisticheskaya Respublika or Belorusskaya SSR), also commonly referred to in English as Byelorussia was a client state of the Soviet Union (USSR).
Bydgoszcz (Polish pronunciation: [ˈbɨdɡɔʂt͡ʂ], German: Bromberg [ˈbʁɔmbɛɐ̯k], Latin: Bydgostia) is a city in northern Poland, on the Brda and Vistula rivers.
BYD Auto Co., Ltd. is a Chinese automobile manufacturer based in Xi'an, Shaanxi Province, and a wholly owned subsidiary of BYD Company.
The Byzantine–Sasanian War of 602–628 was the final and most devastating of the series of wars fought between the Byzantine (Eastern Roman) Empire and the Sasanian Empire of Persia.
Bye Bye Birdie is a stage musical based on a book by Michael Stewart, with lyrics by Lee Adams and music by Charles Strouse.