Developments in direct fluorination are described, which changed our perception of the viability of this methodology for selective introduction of carbon–fluorine bonds. Use of acids as solvent media is a valuable technique for electrophilic fluorination, especially with aromatic systems. Fluorinations of 1,3-dicarbonyl compounds proceed well and techniques for promoting reactivity in other carbonyl derivatives are described. ‘In-situ’ formation of other reagents, e.g. by reaction of fluorine with other halogens and with water, provides convenient methodology for halogenation and oxidation.