In 1945 a report entitled Standards on Piezoelectric Crystals: Recommended Terminologyn was prepared by the Committee on Piezoelectric Crystals and issued by the Institute. The present report involves not only much new material, but also a revision of certain portions of the earlier report. Part I of the 1945 report (corresponding to Part 1 of this Standard) remains unchanged, with the following exceptions: The use of left-handed axes for left crystals is now abandoned (see Sections 1,9, and 1.11 to 1.14); and the 1945 rules for rotated plates are now supplanted by the rules in the present report.