An analytic theory of spinodal decomposition, originally published in Reference [1] and reviewed in [2], is described briefly with emphasis on its limits of validity. This theory is quantitatively consistent with Monte-Carlo simulations [3] of phase separation in the center of the miscibility gap and, like these simulations, exhibits no qualitative distinction between spinodal and nucleation mechanisms in the neighbor-hood of the classical spinodal line. The theory is most useful in connection with experiments in which equilibrium properties of the one-phase system just outside the coherent miscibility gap are measured along with time-dependent small-angle scattering, resistivity, magnetic susceptibility, etc. [4] during decomposition. In particular, direct measurements of the correlation length and diffusion constant are specially valuable. The use of such information in the analysis of experimental data is illustrated by recent results of Goldburg et al. [5] on spinodal decomposition in a two-fluid mixture, 2-6 lutidine and water. These results also demonstrate the importance of a rapid, shallow quench for observation of the actual spinodal reaction.