to its primary than is Jupiter to the Sun. To date, more than 140 EGPs/planets have been discovered, more than 25 of which are in more than 10 multiple systems. 55 Cancri houses a quadruplet [@mcarthur], one of which has a mass near that of Neptune ($\sim$17 Earth masses), $\upsilon$ And house a triplet, and GJ 876 houses a doublet in a two-to-one orbital resonance. (We follow the convention by which the planet’s name is given by the star’s name, with an appended lower-case letter, either b, c, or d, in discovery order.)

The projected masses of the known Doppler planets vary from $\sim$0.06 (!) to above 10 , where is a Jupiter mass, which is 318 Earth masses or roughly $10^{-3}$ solar masses. The more massive objects may be brown dwarfs with a different provenance (see Box). Radial-velocity (Doppler) techniques can not distinguish EGPs and Neptune-mass planets from brown dwarfs. The orbital periods of the known EGPs span a vast range from $\sim$1.2 [*days*]{} to $\sim$12 [*years*]{}, their semi-major axes extend from $\sim$0.022 AU to $\sim$6.0 AU, where an AU is an Astronomical Unit, the distance between the Earth and the Sun, and their orbital eccentricities vary from 0.0 