This paper is an introduction to dry processing techniques such as ion beam etching, rf sputter etching, and plasma etching. A short description of the systems is followed by a comparison of their properties relevant to the fabrication of electronic and optical devices. The comparison includes etch rates and their dependence on various parameters, masking materials and dimensional accuracy in pattern delineation, obtainable aspect ratios, and edge profiles. The paper concludes with some examples of plasma- and ion-etched patterns.