  We review our recent works on the quantum transport, mainly in topological
semimetals and also in topological insulators, organized according to the
strength of the magnetic field. At weak magnetic fields, we explain the
negative magnetoresistance in topological semimetals and topological insulators
by using the semiclassical equations of motion with the nontrivial Berry
curvature. We show that the negative magnetoresistance can exist without the
chiral anomaly. At strong magnetic fields, we establish theories for the
quantum oscillations in topological Weyl, Dirac, and nodal-line semimetals. We
propose a new mechanism of 3D quantum Hall effect, via the "wormhole" tunneling
through the Weyl orbit formed by the Fermi arcs and Weyl nodes in topological
semimetals. In the quantum limit at extremely strong magnetic fields, we find
that an unexpected Hall resistance reversal can be understood in terms of the
Weyl fermion annihilation. Additionally, in parallel magnetic fields,
longitudinal resistance dips in the quantum limit can serve as signatures for
topological insulators.
