Borylation of aryl halides with an inexpensive and atom-economical boron source, pinacol borane, has been developed. This system allows for the conversion of aryl and heteroaryl iodides, bromides, and several chlorides, containing a variety of functional groups, to the corresponding pinacol boronate esters. In addition to the increase in substrate scope, this is the first general method where relatively low quantities of catalyst and short reaction times can be employed.