Fluoroalkanoyl peroxides [RF–C(O)–O–O–(O)C–RF; RF=fluoroalkyl group] decompose homolytically via concerted dissociation of an O–O bond and two C–C bonds, whereas non-fluorinated alkanoyl peroxides decompose via stepwise dissociation of these bonds. The former thus afford an RF˙ radical selectively, which initiates the formation of thermally stable fluorinated polymers without an ester group. In this chapter, the electronic structure of fluoroalkanoyl peroxides and non-fluorinated peroxides is studied computationally using ab initio molecular orbital methods to clarify the unique decomposition behavior of fluorinated peroxides at the molecular level. The present calculations indicate that the bond dissociation energy (BDE) of C–C is significantly lowered by fluorination of an alkyl group, whereas the BDE of O–O is little affected by fluorination. The heat of decomposition is also considerably lowered by fluorination, which is attributed to the lower BDE of the C–C bond. These findings suggest that the strength of the C–C bond would play an essential role in determining the reaction mechanism and kinetics of thermal decomposition of fluoroalkanoyl and alkanoyl peroxides.