Recent polarized deep-inelastic scattering experiments have demonstrated that all of the components of the nucleon may perhaps contribute to its spin. This conclusion has been obtained through detailed measurements of polarized structure functions and direct measurements of polarized parton distributions. Both of these topics will be presented in this paper. However, there remains some open questions on nucleon spin structure such as the role of gluons and the third twist-2 structure function, the so-called transversity which is still an unknown quantity. The future of these topics in view of upcoming experiments will also be discussed. ©2000 American Institute of Physics.