  We present a unified treatment of the Aharonov--Bohm (AB) effect for
two-dimensional multiband electronic systems possessing isotropic band
structures. We propose an integral representation of the AB scattering state of
an electron scattered by an infinitely thin solenoid. Moreover, we derive the
asymptotic form of the AB scattering state and obtain the differential cross
section from that. We found a remarkable result, namely that this cross section
is {\it the same for all isotropic systems} and agrees with that obtained first
by Aharonov and Bohm for spinless free particle systems. To demonstrate the
generality of our theory, we consider several specific multiband systems
relevant to condensed matter physics.
