  This is a brief review on the theoretical interpretation of the Aharonov-Bohm
effect, which also contains our new insight into the problem. A particular
emphasis is put on the unique role of electron orbital angular momentum,
especially viewed from the novel concept of the physical component of the gauge
field, which has been extensively discussed in the context of the nucleon spin
decomposition problem as well as the photon angular momentum decomposition
problem. Practically, we concentrate on the frequently discussed idealized
setting of the Aharonov-Bohm effect, i.e. the interference phenomenon of the
electron beam passing around the infinitely-long solenoid. One of the most
puzzling observations in this Aharonov-Bohm solenoid effect is that the
pure-gauge potential outside the solenoid appears to carry non-zero orbital
angular momentum. Through the process of tracing its dynamical origin, we try
to answer several fundamental questions of the Aharonov-Bohm effect, which
includes the question about the reality of the electromagnetic potential, the
gauge-invariance issue, and the non-locality interpretation, etc.
