  The observation of the quark transversity distribution requires another soft
object sensitive to the quark's transverse spin. Dihadron fragmentation
functions represent a convenient tool to analyze partonic spin, which can
influence the angular distribution of the two hadrons. In particular, the
so-called interference fragmentation functions can be used to probe
transversity both in semi-inclusive deep inelastic scattering as well as
proton-proton collisions. We discuss two single-spin asymmetries sensitive to
transversity in the these two processes, at leading twist and leading order in
alpha_S.
