Bloch oscillations arise when a constant electric field is applied to electrons in a periodic crystal lattice. Instead of accelerating indefinitely, electrons undergo periodic oscillation in both k-space (crystal momentum) and real space, with period TB = h/(eEa). The energy dispersion E(k) = −Δ/2·cos(ka) gives a group velocity that reverses as k reaches the Brillouin zone boundary, causing Bragg reflection. Wannier-Stark ladders are the quantized energy levels of this system. Experimentally observed in semiconductor superlattices and ultracold atoms in optical lattices; damping from scattering suppresses oscillations in ordinary crystals.