The transition rates associated with a particle moving in a double potential well under the influence of thermal noise and friction is considered as a generalization of Kramers’ theory of activated rate processes. We obtain expressions for these transition rates which are valid for all friction and for a general (non-Markovian) interaction between the particle and its thermal environment. Nonthermal equilibrium effects in the steady state distribution in the well as well as effects of trajectories returning unrelaxed from the far wall are explicitly taken into account. The results reduce to all the previously obtained results of the single well model. We use the theory to analyze the experimental results of Hasha, Eguchi, and Jonas.