Low-x Physics in pA Collisions and at the EIC

In this proceeding, I review what we have learned, and what we will be able to learn, about low-x physics from proton nucleus (pA) collisions at RHIC and the LHC, and how this complements future Electron-Ion Collider (EIC) measurements. EIC not only will provide us essential and complementary information about the gluon saturation to the knowledge that we have learned from pA collisions at RHIC and the LHC, it will also allow us to visualize the internal structure of protons and nuclei in a multi-dimensional fashion with unprecedented precision.