The pH value is the most frequently used process variable in analysis. The pH value is of outstanding importance in water and environmental analysis and in almost all sectors of industry. Whether the cheese in a dairy is of the right quality, the water in a drinking water supply causes corrosion damage, or the precipitation in a treatment plant for waste water from an electroplating process occurs at the optimal point, all depend on such parameters as the pH value.This technical publication presents the basic electrochemical relationships and typical applications in a general, easily understood form. In addition, information is provided on the current state of technology with regard to transmitters/ controllers and sensors for this process variable.We try to ensure that the "Information on pH measurement" is always kept fully up to date, and therefore appeal to our readers for feedback and the sharing of experience and knowledge. Any suggestions or contributions to the discussion will be most welcome.