  In this talk, I reviewed the recent theoretical progress towards the
exploration of the gluon saturation phenomenon in $pA$ collisions at both RHIC
and the LHC. Two important pillars of this exploration are the single inclusive
forward hadron productions and forward dihadron correlations, which have both
been computed up to one-loop order within the small-$x$ factorization
formalism. Furthermore, detailed numerical study for the single inclusive
hadron production at next-to-leading order provides us good description of the
low transverse momentum data measured in $dAu$ collisions at RHIC with
significantly reduced uncertainty. In addition, the one-loop calculation for
dihadron productions in $pA$ collisions shows that there is a new type of large
logarithm, which is known as the Sudakov factor, arising in the back-to-back
correlation limit.
