  This White Paper presents the science case of an Electron-Ion Collider (EIC),
focused on the structure and interactions of gluon-dominated matter, with the
intent to articulate it to the broader nuclear science community. It was
commissioned by the managements of Brookhaven National Laboratory (BNL) and
Thomas Jefferson National Accelerator Facility (JLab) with the objective of
presenting a summary of scientific opportunities and goals of the EIC as a
follow-up to the 2007 NSAC Long Range plan. This document is a culmination of a
community-wide effort in nuclear science following a series of workshops on EIC
physics and, in particular, the focused ten-week program on "Gluons and quark
sea at high energies" at the Institute for Nuclear Theory in Fall 2010. It
contains a brief description of a few golden physics measurements along with
accelerator and detector concepts required to achieve them, and it benefited
from inputs from the users' communities of BNL and JLab. This White Paper
offers the promise to propel the QCD science program in the U.S., established
with the CEBAF accelerator at JLab and the RHIC collider at BNL, to the next
QCD frontier.
