Abstract. The decay rate of the false vacuum in scalar field theory has the form A Exp(-B). In a famous paper from 1977 Coleman laid down the theory to compute the coefficient B. In a subsequent paper with Callan, they set up the recipe to compute the pre-factor A, but did not manage to compute it explicitly. In their own words: "we are not able to obtain a closed-form expression for A; we are stymied by an obdurate functional determinant". In this talk I explain how my collaborators and I recently found such a closed-form expression for A in the thin-wall approximation.