T1

T1 may refer to many things including:
 * Digital Signal 1, originally over a "T1" interoffice facility or "Transmission Level 1" telecommunications line in North America and Japan
 * T1 General tax form used in Canada for personal tax returns
 * First thoracic vertebra of the vertebral column or T1 spinal nerve, in human anatomy
 * Cork encoding (or T1 encoding) is a character encoding
 * UltraSPARC T1 microprocessor made by Sun Microsystems
 * PRR T1, an innovative duplex locomotive developed by the Pennsylvania Railroad
 * The Caparo T1, a British supercar
 * The Ford T1 platform

T-1 may refer to:
 * T-1 Jayhawk, a twin-engined jet aircraft used by the United States Air Force
 * Terrible One, BMX company
 * A code used in deniable operations by intelligence and security agencies. A 'T1' code orders a kill. For example, a 'T104' means kill without trace. The codes are used when transferring encrypted messages, and to avoid actually ordering an assassination, which is not officially legal for some agencies. Evidence of T104 messages is often destroyed itself.
 * A trade name for A514 steel
 * Fuji T-1, a Japanese trainer aircraft
 * T-carrier, a class of digital networking connections
 * T-1 (Terminator character), a fictional robot appearing in the film Terminator 3: Rise of the Machines

T₁ may refer to:
 * A mathematical property of the topological T₁ spaces
 * T1 is the Spin-lattice relaxation time in MRI and NMR

T1 T1 T1 T1 T-1 T1 T 1