We study the role of electron-electron interactions near integer and abelian fractional quantum Hall (QH) transitions using composite fermion (CF) representations. Interaction effects are encapsulated in CF theories as gauge fluctuations. Without gauge fluctuations, the CF system realizes a `dual' representation of the noninteracting QH transition. With gauge fluctuations, the system is governed by a gauged nonlinear sigma model (NLSM) with a $\ensuremath{\theta}\phantom{\rule{0.28em}{0ex}}\mathrm{term}$. While the transition is described by a strong-coupling fixed point of the NLSM, we are nevertheless able to deduce two of its properties. With
1/r interactions, (1) the transition has a dynamical exponent
z=1, and (2) all transitions are ``superuniversal'': fractional and integer QH transitions are in the same universality class. With short-range interactions,
z=2 and the fate of superuniversality remains unclear.
Superuniversality is the sharing of the same critical exponents among distinct critical points. This surprising behavior is observed at phase transitions between various quantum Hall states found in the two-dimensional electron gas. Motivated by the theoretical challenge posed by superuniversality, we introduce a new effective description that has an emergent
U(N) gauge symmetry with
N>1 for a quantum phase transition between an integer quantum Hall state and an insulator. We use modular transformations to generate from this theory new effective descriptions for quantum phase transitions between a large class of fractional quantum Hall states whose quasiparticle excitations have abelian statistics. In the 't Hooft large
N limit, the correlation length and dynamical critical exponents are independent of the particular transition in the absence of disorder. We argue that this conclusion survives away from the large
N limit using recent duality conjectures and, thereby, provide theoretical support for the phenomenon of superuniversality found at distinct quantum Hall critical points.