For Photography: Zone System - Explains about zone system including visualisation, exposure, technique, and application to black and white and colour roll film and digital photography.
SR Photogaphy: The Zone System - Information is taken from 'The Zone System - A Basic Explanation' by Arsene Baquet and Steve Holtz.
Using the Zone System in the Field - Article on zone system to control exposure and contrast of photographs. By Bob Hitchman from Apogee Photo Magazine.
Wikipedia: Zone system - Article on zone system, a photographic technique to get optimal film exposure and development.