An overview of the measured transport properties of the two
dimensional electron fluids in high
mobility semiconductor devices with low electron densities
is presented as well as some of the theories
that have been proposed to account for them. Many features
of the observations are not easily
reconciled with a description based on the well understood
physics of weakly interacting quasiparticles
in a disordered medium. Rather, they reflect new physics
associated with strong correlation effects,
which warrant further study.