Theoretical and experimental research on general relativity with torsion is reviewed. An introductory section establishes definitions and notation, introduces tetrads, the anholonomic formulation and the Dirac equation in curved space with torsion. After that, gauge theories of gravitation are introduced, starting with local Poincaré gauge theory, in which the torsion arises as a translational gauge field strength, and other gauge approaches are described. Torsion that is derived from a potential, including a scalar, vector, and tensor potential is discussed, with emphasis on the antisymmetric tensor of the string theory kind. Teleparallel theories are described, conformal invariance is discussed and a brief section on the equation of motion is presented. Experiments that have searched for, or bounded, torsion are described and the possible physical manifestations are broken down into the broad areas of quantum effects, laboratory scale phenomena and large-scale tests. Finally, a discussion of the relationship between string theory and torsion is presented.