Theoretical descriptions for the reactions of halo nuclei are reviewed. Dep
ending on the projectile incident energy as well as the reaction mechanisms
, several theoretical frameworks have been developed for the reactions of h
alo nuclei. They are presented in a systematic way to elucidate their mutua
l relationship. The Glauber's multiple scattering theory is adequate to des
cribe the high energy reactions. The theory is applied to the integrated cr
oss sections such as interaction and neutron removal cross sections, and al
so to the momentum distribution of the fragment nucleus. A few-body direct
reaction model is appropriate to describe the medium energy reactions. This
is applied to the elastic scattering of halo nuclei and to construct their
optical potentials. For the Coulomb breakup reactions, theoretical treatme
nts are developed in the time-dependent Schodinger equation with and withou
t the perturbation approximation. A direct approach to solve the equation i
s applied to analyze the postacceleration mechanism in the Coulomb breakup
process. Finally a fusion reaction of the halo nuclei is discussed with a t
hree-body model.