  Associated particle production processes in pp and heavy ion collisions at
the LHC are in particular interesting in the sense that they provide unique
tools to study double parton scattering (DPS) mechanism. In this talk, I will
first review the recent theoretical, phenomenological and experimental
developments of DPS in pp collisions. Then, I will focus on the DPS studies in
heavy ion collisions, and stress their roles in understanding the cold nuclear
matter effects, such as the (poorly known) impact-parameter dependent nuclear
parton densities.
