Validity of flavor symmetry and charge symmetry for parton distributions

Measurements of the Gottfried Sum Rule suggest significant violation of flavor symmetry in the proton sea. This has recently been confirmed in measurements of pp and pD Drell-Yan processes by the E866 experiment. We review the question of flavor symmetry violation, and possible theoretical explanations of this effect. The interpretation of large flavor symmetry violation rests on the assumption of parton charge symmetry. Our model calculations suggest charge symmetry violation [CSV] for parton valence distributions of a few percent. We review present experimental limits on CSV, and we suggest new experiments which might detect parton CSV.