Recently, the CMS experiment at CERN reported the observation of a long-range, near-side two-particle correlation in proton-nucleus (pA) collisions at the Large Hadron Collider. This phenomenon, known as the "Ridge", was first seen in high energy nucleus-nucleus (AA) collisions at RHIC. It is believed to be related to the collective evolution of a strongly interacting QCD matter. Unexpectedly, a long-range ridge correlation has also been observed later in very small system of proton-proton (pp) collisions for the rare high multiplicity events. Remarkably, predictions in the framework of Color Glass Condensate are found to well describe both the pp and pA data, in absence of any collective flow effect. I will first present the recent experimental observation of the ridge in pA from CMS. The state-of-the-art theoretical interpretations of this phenomenon will be discussed, with the emphasis on the potential connection of pp, pA and AA systems. An outlook to future studies on this topic will be given in light of the upcoming high-intensity pA run in January 2013.