  We present the complete leading-order results for the azimuthal dependences
and polarization observables in $e^+e^-\to h_1 h_2 + X$ processes, where the
two hadrons are produced almost back-to-back, within a transverse momentum
dependent (TMD) factorization scheme. We consider spinless (or unpolarized) and
spin-1/2 hadron production and give the full set of the corresponding quark and
gluon TMD fragmentation functions (TMD-FFs). By adopting the helicity
formalism, which allows for a more direct probabilistic interpretation, single-
and double-polarization cases are discussed in detail. Simplified expressions,
useful for phenomenological analyses, are obtained by assuming a factorized
Gaussian-like dependence on intrinsic transverse momenta for the TMD-FFs.
