BTB

BTB may refer to:

In biology:
 * Blood–testis barrier in testicular anatomy
 * Blood–thymus barrier
 * Bovine tuberculosis or Mycobacterium bovis, a disease originating 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)