Electrophilic substitution reactions on saturated carbons are extremely rare. Elemental fluorine, however, uses this pathway to replace tertiary unactivated hydrogens with great regio- and stereoselectivity, resulting in a full retention of configuration. In accordance with the proposed mechanism, the higher the contribution of p orbitals to the tertiary C-H bond, the easier the substitution process becomes. On the other hand, a low degree of p hybridization such as with cyclopropyl hydrogens, or due to the close proximity of an oxygenated function, does not allow any electrophilic substitution. Competitive reactions between tertiary hydrogens, either in different or in the same molecule, emphasize the electronic factors that govern this reaction. Oxygen- as well as nitro-gen-containing molecules can participate in the reaction providing they are suitably protected. Chemically inert paraffins also react readily with fluorine in similar fashion producing monofluorinated derivatives. Methods for either acidic or basic dehydrofluorination were developed, resulting in double bond formation, thus opening an excellent route for further chemical transformations at sites where no chemical reactions were previously possible.