The Hall resistivity has long been used to characterize the sign and density of mobile charge carriers in metals. However, traditional Fermi-liquid and Boltzmann transport theory have failed to explain ‘’Hall anomalies’’ which have been observed in many strongly correlated systems, including high Tc superconductors. Recently we derived formulas for the Hall coefficient, and a revised theory of flux flow in superconductors which can explain such Hall sign reversals, and to elucidate the ‘’moving parts’’ of the current in the presence of strong electronic correlations.