Highly enantioselective halolactonizations have been developed that. employ a chiral proton catalyst-N-iodosuccinimide (NIS) reagent system in which the Bronsted acid is used at catalyst loadings as low as 1 mol %. An approach that modulates the achiral counterion (equimolar to the neutral chiral ligand-proton complex present at low catalyst loadings) to optimize the enantioselection is documented for the first time in this transformation. In this way, unsaturated carboxylic acids are converted to gamma-lactones in high yields (up to 98% ee) using commercially available NIS.