Separation of gaseous molecules in supersonic free jets by laser-assisted selective condensation repression is reviewed. It is shown to have evolved from Becker's pre-laser "Nozzle Separator" concept of 1956 by simple addition of a laser. Although useful to separate mixtures of dissimilar gases, the technique has mostly been applied to isotope separation. To enrich (SF6)-S-i for example, SF6 mixed with an inert carrier gas G is expanded through a nozzle into a low-pressure chamber, where it forms a supersonic, jet and creates van der Waals hetero- or homodimers SF6:G and SF6:SF6 if T < 150 K. By coaxial or cross irradiation of the free jet with a tunable laser, dimerization of selectively excited (SF6)-S-j is prevented. As radial out-of-the-jet-core diffusion depends on molecular mass, nondimerizable laser-excited (SF6)-S-j monomers enrich the background "rim" gases, which are separated by a skimmer from much heavier nonexcited (SF6)-S-i:G and (SF6)-S-i:SF6 dimers in the jet's core. (C) 2010 American Institute of Chemical Engineers AIChE J, 56: 2331-2337, 2010