Transversity and Spin Structure Functions

Measurements of single-spin asymmetries for semi-inclusive electro-production of pions and kaons in deep-inelastic scattering with transverse target polarization open a new window on the transverse quark and gluon structure of the nucleon. The first experimental results from such measurements as well as experiments in progress are discussed. Properties of the spin-dependent Collins fragmentation function and prospects for extracting the transversity are reviewed and evidence for nonzero Sivers asymmetries as manifestations of quark orbital angular momentum is evaluated.