  We present an effective elastic theory which {\em quantitatively} describes
the stripe phase of the two-dimensional electron gas in high Landau levels
($N\geq2$). The dynamical matrix is obtained with remarkably high precision
from the density-density correlation function in the time-dependent
Hartree-Fock approximation. A renormalization group analysis shows that at T=0,
as the partial filling factor $\Delta\nu\equiv\nu-\lfloor\nu\rfloor$ moves away
from 1/2, the anisotropic conducting state may undergo quantum phase
transitions: stripes may get pinned along their conducting direction by
disorder, or may lock into one another to form a two-dimensional crystal. The
model predicts values of $\Delta\nu$ for each transition. The transitions
should be reflected in the temperature dependence of the dissipative
conductivity.
