BTB
BTB may refer to:
In biology:
- Blood–testis barrier in testicular anatomy
 - Blood–thymus barrier
 - bTB, bovine tuberculosis or Mycobacterium bovis, a disease in cattle
 - Breakthrough bleeding, of the menstrual period
 - Bromothymol blue, a chemical indicator for weak acids and bases
 - BTB/POZ domain, a protein domain
 
In other uses:
- Belgian Union of Transport Workers, a trade union in Belgium
 - Branch target buffer, a computer processor element
 - Bétou Airport, in the Republic of the Congo (IATA airport code: BTB)
 - Basil Temple Blackwood (1870–1917), British book illustrator (credited as B.T.B.)
 - Bob the Builder, British children's television series
 - Board-to-board connector (BTB)