The Driftless Area of southwestern Wisconsin and northwestern Illinois got its name from the lack of glacial sediment ("drift") covering the landscape. The surficial geology and topography of the Driftless Area are thus distinct from the surrounding region where multiple phases of glaciation left their mark. This pamphlet, a collaborative effort between four neighboring state geological surveys, describes and outlines the boundary of the unglaciated Driftless Area based on modern geologic evidence.