In the course of developing techniques for ion−beam etching of solid bulk materials and thin deposited films, we undertook a systematic investigation of etch rates of several materials and the dependence of etch rate on beam parameters and beam angle of incidence. Results of these measurements are presented. Under certain conditions, cones formed on the surface being etched. An explanation for this instability phenomenon is given. In most practical applications of ion−beam etching, suitable masking techniques are necessary. We have developed procedures for photoresist masking for two classes of etching: (a) high−resolution, shallow−depth etching (typical dimension ∠1 μ); (b) low−resolution, very deep etching (typical dimension ∠50 μ). The methods used will be discussed, and in particular we will consider the influence of redeposition of sputtered material and the profile of the photoresist on the final−etched wall shape.