  It is argued that there are strong similarities between the infra-red physics
of N=2 supersymmetric Yang-Mills and that of the quantum Hall effect, both
systems exhibit a hierarchy of vacua with a sub-group of the modular group
mapping between them. The scaling flow for pure SU(2) N=2 supersymmetric
Yang-Mills in 4-dimensions is re-examined and an earlier suggestion in the
literature, that was singular at strong coupling, is modified to a form that is
well behaved at both weak and strong coupling and describes the crossover in an
analytic fashion. Similarities between the phase diagram and the flow of SUSY
Yang-Mills and that of the quantum Hall effect are then described, with the
Hall conductivity in the latter playing the role of the theta-parameter in the
former. Hall plateaux, with odd denominator filling fractions, are analogous to
fixed points at strong coupling in N=2 SUSY Yang-Mills, where the massless
degrees of freedom carry an odd monopole charge.
