The M-theory Three-Form and ADE Gauge Symmetry

M- and F-theory compactifications with ADE singularities give rise to non-abelian ADE gauge symmetries. The physical explanation for this phenomenon involves M2-branes wrapped on vanishing cycles. We consider an alternative approach which relies on relating the M-theory three-form to the Chern-Simons form of a bundle, and allows us to address some outstanding questions.