The rates of thermolysis of alpha,alpha-difluoro beta-lactones 1, leading to CO(2) and 1,1-difluoro olefins, have been obtained in the gas phase and in solution, and the activation parameters are reported. Ab initio calculations on the fluoro and nonfluorinated beta-lactone systems are also reported. The gas-phase kinetic and theoretical results are discussed in terms of a probable concerted, asynchronous, nonpolar mechanism, whereas the solution kinetics, which include extensive solvent effect studies, are discussed in terms of a polar mechanism which probably involves formation of a zwitterionic intermediate.