  The recent theoretical and experimental activities in positronium (Ps)
scattering by atoms and molecules are reviewed with special emphasis at low
energies. We critically compare the results of different groups $-$ theoretical
and experimental. The theoretical approaches considered include the $R$-matrix
and close-coupling methods applied to Ps-H, Ps-He, and Ps-Li scattering, and a
coupled-channel approach with a nonlocal model-potential for Ps scattering by
H, He, H$_2$, Ne, Ar, Li, Na, K, Rb, Cs, and Ps and for pickoff quenching in
Ps-He scattering. Results for scattering lengths, partial, total and
differential cross sections as well as resonance and binding energies in
different systems are discussed.
