The efficiency and selectivity of two approaches for introducing alkoxysilane functionality to polyethylene (PE) are examined along with the moisture-curing performance of the resulting products. Although the peroxide-initiated grafting of vinyltriethoxysilane to PE is accompanied by undesirable crosslinking, comparable silane contents can be introduced without affecting the melt viscosity through the addition of mercaptopropyltriethoxysilane (MPTES) to the unsaturation within the polymer. Rapid hydrogen atom donation by thiols underlies this unique selectivity for grafting versus molecular weight alteration, and gives rise to a remarkable tolerance of MPTES additions to phenolic antioxidants. Direct comparisons of the moisture-curing efficiencies provided by the two functionalization techniques reveal few significant differences in crosslink yields or composition distributions.