Abstract The measurement of the earth’s gravity field, whether in absolute or relative terms, is one of mankind’s greatest engineering achievements, the accuracy of which can be on the order of one part in one billion of the earth’s total field. During a period of more than one century, numerous instruments have been invented, many of which have met with large commercial success. It is not within the scope of this book to review the extensive history of gravity instruments or to give details of instruments that are not now in use. A complete description of all gravimeters mentioned in this chapter and many others not mentioned here can be found in Nabighian et al. (2005), along with their advantages and limitations. In this chapter, we discuss absolute and relative instruments, gravity gradiometry, field operations, measurement uncertainty, and ambiguity related to survey design.