Catalytic quantities of indium(III) triflate (In(OTf)₃) efficiently promote transacetalisation reactions of glycerol with acyclic acetals to generate the corresponding cyclic acetals under solvent-free reaction conditions. The protocol is rapid and employs very mild reaction conditions. Unreactive ketones, such as acetophenone or benzophenone, undergo efficient acetalisation in the presence of In(OTf)₃ and trimethyl orthoformate (TMOF) to give high conversions of the corresponding glycerol acetals.