  We present a systematic classification of field directions for the
string-derived flipped SU(5) model that are D- and F-flat to all orders.
Properties of the flipped SU(5) model with field values in these directions are
compared to those associated with other flat directions that have been shown to
be F-flat to specific finite orders in the superpotential. We discuss the
phenomenological Higgs spectrum, and quark and charged-lepton mass textures.
