By or BY may refer to:

• Bye (sports) or by, a free pass through a round of competition in a tournament
• CC-BY, a Creative Commons attribution license
• Budget Year (BY), a synonym for Fiscal Year
• By, Doubs, a commune in the Doubs département of France
• By, Norway, a village in the municipality of Åfjord, Norway
• Bavaria's official abbreviation
• Burundi's FIPS Pub 10-4 and obsolete NATO digram country code
• Belarus's ISO country code
  • .by, the ccTLD for Belarus
• Byelorussian Soviet Socialist Republic's ISO country code
• Thomsonfly's IATA airline code

.by is the Internet country code top-level domain (ccTLD) for Belarus. It is administered by The Operative-analytical center of the Republic of Belarus (Оперативно-аналитический центр при Президенте Республики Беларусь.). The code "BY" originates from "Byelorussia", which is the transcription of the Russian name for the country (Белоруссия), Russian being Belarus' most commonly used language. It was officially used during their inclusion in the Soviet Union. The ccTLD was created for Belarus on May 10, 1994.