The making and breaking of nanometer-scale contacts is an essential operation in MEMS devices with moving parts. The behavior of contacts in this size range is not well understood, especially if viscoelastic materials are involved. This article describes shear modulation spectroscopy, a new scanning force microscope technique especially well suited for quantitative studies of nanometer-scale contacts to viscoelastic materials such as lubricants and some polymers. The technique is illustrated by measurements and analysis of contacts to poly(vinylethylene).