  By analyzing the temperature ($T$) and density ($n$) dependence of the
measured conductivity ($\sigma$) of 2D electrons in the low density
($\sim10^{11}$cm$^{-2}$) and temperature (0.02 - 10 K) regime of high-mobility
(1.0 and 1.5 $\times 10^4$ cm$^2$/Vs) Si MOSFETs, we establish that the
putative 2D metal-insulator transition is a density-inhomogeneity driven
percolation transition where the density-dependent conductivity vanishes as
$\sigma (n) \propto (n - n_p)^p$, with the exponent $p \sim 1.2$ being
consistent with a percolation transition. The `metallic' behavior of $\sigma
(T)$ for $n > n_p$ is shown to be well-described by a semi-classical Boltzmann
theory, and we observe the standard weak localization-induced negative
magnetoresistance behavior, as expected in a normal Fermi liquid, in the
metallic phase.
