  Experiments performed over the last twenty years have revealed striking
similarities between several two-dimensional (2D) fermion systems, including
diluted two-dimensional electron liquids in semiconductors, 3He monolayers, and
layered organic charge-transfer salts. These experimental results, together
with recent theoretical advances, provide compelling evidence that strong
electronic correlations - Wigner-Mott physics - dominate the universal features
of the corresponding metal-insulator transitions (MIT). Here we review the
recent theoretical work exploring quantum criticality of Mott and Wigner-Mott
transitions, and argue that most puzzling features of the experiments find
natural and physically transparent interpretation based on this perspective.
