Despite many decades of experimentation and theoretical progress in QCD, we are still far from understanding the precise role gluons (and sea quarks) play in imparting the properties to nucleons and nuclei. We now realize that many of them are emergent properties resulting from the partons' collective behavior. Over the past decade, theorists have developed sophisticated tools and formalisms to view and understand the nucleons and nuclei in terms of that collective interactions of partons. A high energy high luminosity polarized electron ion collider coupled with appropriately designed detector systems would allow us to study the gluons and sea quarks within the framework of those new theoretical tools. Technology to achieve the desired design parameters of such a collider seems to be on the horizon. Motivated by the anticipated readiness of all three: theory, accelerator and detector capabilities, in the next few years, the US Nuclear Science Advisory Committee (NSAC) recommended in 2015 that an electron ion collider (EIC) be built. I will review the compelling open questions in QCD that will be addressed by the EIC, and give a brief overview of where we stand on it in terms of the project (accelerator and detector designs) and collaboration building.

Argonne Physics Division Colloquium Schedule