  We report on the extraction of dihadron fragmentation functions (DiFF) from
the semiinclusive production of two hadron pairs in back-to-back jets in e+e-
annihilation. A nonzero asymmetry in the correlation of azimuthal orientations
of opposite $\pi^+\pi^-$ pairs is related to the transverse polarization of
fragmenting quarks through a significant polarized DiFF. A combined analysis of
this asymmetry and the spin asymmetry in the SIDIS process $ep^{\uparrow}\to
e'(\pi^+\pi^-)X$ has led to the first extraction of the u and d-flavor
transversity parton distribution function in the framework of collinear
factorization.
