Palladium-catalyzed regioselective Heck arylation of the electron-rich olefins. vinyl ethers lad, enamides 1 e-g, and allyltrimethylsilane 1 h, has been accomplished in imidazolium ionic liquids with a wide range of aryl bromides and iodides instead of the commonly used. but commercially unavailable and expensive, aryl triflates. The reaction proceeded with high efficiency and remarkable regioselectivity without the need for costly or toxic halide scavengers, leading exclusively to substitution by aryl groups of diverse electronic and steric properties at the olefinic carbon a to the heteroatom of 1 a-g and beta to the heteroatom of 1 h. In contrast, the arylation reaction in molecular solvents led to mixtures of regioisomers under similar conditions. Several lines of evidence point to the unique regiocontrol stemming from the ionic environment provided by the ionic liquid that alters the reaction pathway. The chemistry provides a simple, effective method for preparing branched, arylated olefins and contributes to the extension of Heck reaction to a wider range of substrates.