  Weak localization and weak anti-localization are quantum interference effects
in quantum transport in a disordered electron system. Weak anti-localization
enhances the conductivity and weak localization suppresses the conductivity
with decreasing temperature at very low temperatures. A magnetic field can
destroy the quantum interference effect, giving rise to a cusp-like positive
and negative magnetoconductivity as the signatures of weak localization and
weak anti-localization, respectively. These effects have been widely observed
in topological insulators. In this article, we review recent progresses in both
theory and experiment of weak (anti-)localization in topological insulators,
where the quasiparticles are described as Dirac fermions. We predicted a
crossover from weak anti-localization to weak localization if the massless
Dirac fermions (such as the surface states of topological insulator) acquire a
Dirac mass, which was confirmed experimentally. The bulk states in a
topological insulator thin film can exhibit the weak localization effect, quite
different from other system with strong spin-orbit interaction. We compare the
localization behaviors of Dirac fermions with conventional electron systems in
the presence of disorders of different symmetries. Finally, we show that both
the interaction and quantum interference are required to account for the
experimentally observed temperature and magnetic field dependence of the
conductivity at low temperatures.
