The Spin Structure of the Nucleon
  This article reviews our present understanding of QCD spin physics: the proton spin puzzle and new developments aimed at understanding the transverse structure of the nucleon. We discuss present experimental investigations of the nucleon's internal spin structure, the theoretical interpretation of the different measurements and the open questions and challenges for future investigation. 
Christine A. Aidala, Steven D. Bass, Delia Hasch, Gerhard K. Mallot
hep-ph hep-ex nucl-th