Rayleigh waves in partially saturated layered half-spaces are investigated under plane strain conditions. The analytical model is based on Biot's theory of wave propagation in porous fluid-saturated media. The dispersion relation is derived using methods from propagation of free waves in layered media. For limiting cases of the dimensionless frequency, it is shown that the problem reduces to more simplified forms discussed in previous works. Further, it is shown that for zero pore pressure, the problem reduces to known results of elastodynamics.