The properties of strongly correlated electron models in the form of ladders are reviewed. The groundstate of undoped and lightly doped two chain ladders described by the t-J model is a realization of a d-wave resonance valence bond state. Although many properties are those of lightly doped insulators, the strong magnetic polarizability modifies the dispersion relation for quasiparticles to resemble a metal with a large Fermi surface. Some discussion is given of possible relationships of the ladder systems to a two dimensional planar t-J model and of a possible origin of the spin-gap in underdoped cuprates.