In the study of the QCD theory at high energy, an interesting kinematic region is the small-x saturation limit. An effective theory that describes the dynamics of partons in high density systems and the phenomenon of gluon saturation at small x is the Color Glass Condensate (CGC) theory. At the saturation level, a proper description of the gluon dynamics naturally requires knowledge of the transverse momentum of the gluons and of their distributions in all three momentum components, these are referred to as Transverse momentum dependent parton distributions (TMDs). Lately, there are also progress to know the contributions coming from the small x domain to the spin physics of protons.

In this talk we will review the QCD behaviour in the small-x formalism, particularly- QCD evolutions, gluon saturation, TMD PDFs, proton spin puzzle – broadly the physics for the upcoming Electron-Ion Collider (EIC).