An overview is given over the photometric transit method for the detection of extraterrestrial planets. Discussed are: its basic principals, its derivable parameters, requirements for its implementation, and sources of confusion. Special emphasis is given space based experiments that may lead towards the detection of Earth-like planets. The detection of large moons may also be possible, either by their direct detection in the shape of a transit lightcurve, or by their influences on the mid-time of transit. For the latter point, estimations are given on the potential that will offer the upcoming three space mission, COROT by CNES, Kepler by NASA and Eddington by ESA for the detection of moons around extrasolar planets. By a similar principle, measurements of variations in the exact minimum time of eclipsing binaries are also expected to lead to a large number of detections of circumbinary planets.