The abundances of polymeric species of the alkali fluorides in the vapor phase and their dissociation energies have been determined by use of the method of Miller and Kusch. For LiF, NaF, KF, RbF, and CsF, the dissociation energies of the dimer are 58.9, 54.3, 47.6, 42.0, and 37.8 kcal/M, respectively. For LiF the trimer was also observed, with a dissociation energy of 38.3 kcal/M. When the salt is in equilibrium with its vapor at a temperature where the vapor pressure is 10-2 mm of Hg, the abundance of the dimer decreases in the sequence from LiF to CsF. The heats of sublimation for the various species were also found.