In this review, we discuss the angular anisotropies in the scattering facto
rs of electrons and positrons for scattering by atoms in solids. We show th
at, as a function of the angle, the maximum number of dips in the scatterin
g factor's magnitude and jumps of near pi in its phase are related to the a
ngular momenta of the bound and resonance states of the potential. The effe
ct of the scattering factor's anisotropies on low-energy electron and posit
ron holographic wave-front reconstruction is discussed.