Experimental and theoretical work is reviewed on the two-dimensional system of electrons suspended above
the surfaces of certain cryogenic dielectrics (liquid 3He and 4He and liquid and solid hydrogen) by the image
force and an external electrostatic field. The stability of the system is studied. The electron properties
determined by the interactions of the electrons with each other, with vapor atoms, and with thermal
vibrations of the liquid surface are studied. A study of nonlinear effects is reported.