  We describe how bi-maximal neutrino mixing can be realized in realistic
models based on MSSM and SUSY GUTs such as SU(5) and SO(10). A crucial role is
played by an anomalous ${\cal U}(1)$ flavor symmetry, which also helps
understand the observed charged fermion mass hierarchies and the magnitudes of
the CKM matrix elements. While in MSSM a variety of solutions for the solar
neutrino puzzle are possible, SUSY SU(5) and SO(10) only permit the large
mixing angle MSW solution. Models in which the ${\cal U}(1)$ symmetry also
mediates SUSY breaking allow both the large mixing angle and the low MSW
solutions.
  We also present renormalization group studies for the neutrino mass matrix,
generated through the ${\cal U}(1)$ flavor symmetry. Our analysis shows that
renormalization does not change the desirable picture of bi-maximal mixing.
