This glossary is a revision of “Definitions of Terms Used in Geodetic and Other Surveys” (U.S. Coast and Geodetic Survey Special Publication 242) by Hugh C. Mitchell, published in 1948 by the U.S. Government Printing Office. Since Mitchell’s book appeared, the standards, instruments, theory, and procedures of that time have been markedly changed, complemented, reduced in importance, or completely replaced by new ones. In addition, the interaction of geodesy with other disciplines has greatly increased, which demands that these relationships be covered also. Examples of the considerable changes since 1948 can be found in almost every single page of this glossary. Invar tapes have been mostly replaced by electronic devices which employ light, infrared, or radio waves. Photogrammetry has become an important method of acquiring geodetic information. Observations on artificial satellites have become a dominant source for information on both geometric positioning and the determination of the gravity field. The computational aspects of geodesy have been just as heavily affected. Adjustment by solving for angles and distances has been superseded by solving for coordinates. Forms that depended on tables or mechanical calculators have disappeared in this age of electronic computers. The geodetic datums of 40 years ago are of interest today mainly to historians. Such a variety of changes and additions has swelled the number of definitions from 800 to almost 5,000. Even this sixfold increase will omit many terms which should be rightfully included, but are missing because it was well-nigh impossible to keep up with the rapid innovation in geodetic theory and practice. For example, the revolution in geodetic positioning due to the implementation of the Global Positioning System (GPS) is barely touched on here; the enrichment to the geodetic vocabulary entailed by GPS will have to be documented in a future edition. The expansion in size of this glossary covers only a small part of the material available and considered. Selections had to be made, and the judgments reflect the inevitable biases of the compilers. In addition, users are bound to discover terms which are inexplicably missing. The reason for this is simple: human imperfection. Correspondence noting errors, omissions, or containing suggestions are welcomed in anticipation of a future set of addenda and corrigenda.