A stochastic many-particle approach is applied to study the kinetics of reversible excimer formation in solution. Coupled dynamic equations for the macroscopic concentrations and for the radial distribution function are derived, anti applied to analyze : (i) time resolved kinetics after a short pulse, and (ii) steady-state kinetics. Renormalization of the phenomenological excimer;dissociation rate coefficient due to nonequilibrium effects is discussed. A relation is demonstrated between steady-state, i eversible monomer-excimer kinetics and irreversible; fluorescence kinetics. Explicit results are given for the excimer fluorescence yield, assuming the Smoluchowski-Collins-Kimball reactivity model.