Multiple parton interaction is an important component of the perturbative QCD 
(pQCD) formulation, from gauge invariance, transverse-momentum-dependent (TMD) 
parton distributions to higher-twist contributions. In this talk, I will 
review the role of multiple parton interaction in the generalized factorization
 framework of pQCD and use the deeply inelastic scattering (DIS) as an example 
to discuss the consequences of multiple parton interaction in pQCD processes, 
which in term can shed light on structures of hadrons, nuclei and quark-gluon 
plasma.