The field-scale application of apparent soil electrical conductivity (EC a) to agriculture has its origin in the measurement of soil salinity, which is an arid-zone problem associated with irrigated agricultural land and with areas having shallow water tables. Apparent soil electrical conductivity is influenced by a combination of physico-chemical properties including soluble salts, clay content and mineralogy, soil water content, bulk density, organic matter, and soil temperature; consequently, measurements of EC a have been used at field scales to map the spatial variation of several edaphic properties: soil salinity, clay content or depth to clay-rich layers, soil water content, the depth of flood deposited sands, and organic matter. In addition, EC a has been used at field scales to determine a variety of anthropogenic properties: leaching fraction, irrigation and drainage patterns, and compaction patterns due to farm machinery. Since its early agricultural use as a means of measuring soil salinity, the agricultural application of EC a has evolved into a widely accepted means of establishing the spatial variability of several soil physico-chemical properties that influence the EC a measurement. Apparent soil electrical conductivity is a quick, reliable, easy-to-take soil measurement that often, but not always, relates to crop yield. For these reasons, the measurement of EC a is among the most frequently used tools in precision agriculture research for the spatio-temporal characterization of edaphic and anthropogenic properties that influence crop yield. It is the objective of this paper to provide a review of the development and use of EC a measurements for agricultural purposes, particularly from a perspective of precision agriculture applications. Background information is presented to provide the reader with (i) an understanding of the basic theories and principles of the EC a measurement, (ii) an overview of various EC a measurement techniques, (iii) applications of EC a measurements in agriculture, particularly site-specific crop management, (iv) guidelines for conducting an EC a survey, and (v) current trends and future developments in the application of EC a to precision agriculture. Unquestionably, EC a is an invaluable agricultural tool that provides spatial information for soil quality assessment and precision agriculture applications including the delineation of site-specific management units. Technologies such as geo-referenced EC a measurement techniques have brought precision agriculture from a 1980's concept to a promising tool for achieving sustainable agriculture.