Atomic layer etching (ALE) is a technology promising to meet the requirement of atomic scale fidelity for manufacturing of integrated devices of the 10-nm node and below. In analogy to atomic layer deposition, ALE is characterized by the separation of process steps. What makes it ALE is that these process steps are as saturated as possible, which means they are based on self-limiting reactions. This definition of ALE encompasses a wide variety of etching schemes including reactants delivered by gases, plasma, liquid chemistry, or other sources. It is also very flexible with respect to the source of energy for the removal step. This entry is focused on directional ALE with surface modification via chemisorption, conversion, and deposition and removal by ions or fast non-reactive neutrals. The ion and neutral fluxes are separated in the time domain.