  The complete knowledge of the nucleon spin structure at leading twist
requires also addressing the transverse spin distribution of quarks, or
transversity, which is yet unexplored because of its chiral-odd nature.
Elaborating strategies to extract it from (spin) asymmetry data represents a
unique opportunity to explore more generally the transverse spin structure of
the nucleon and the transverse momentum dynamics of partons inside it. Here, we
critically review some of the most promising approaches.
