  This report describes the physics case, the resulting detector requirements,
and the evolving detector concepts for the experimental program at the
Electron-Ion Collider (EIC). The EIC will be a powerful new high-luminosity
facility in the United States with the capability to collide high-energy
electron beams with high-energy proton and ion beams, providing access to those
regions in the nucleon and nuclei where their structure is dominated by gluons.
Moreover, polarized beams in the EIC will give unprecedented access to the
spatial and spin structure of the proton, neutron, and light ions. The studies
leading to this document were commissioned and organized by the EIC User Group
with the objective of advancing the state and detail of the physics program and
developing detector concepts that meet the emerging requirements in preparation
for the realization of the EIC. The effort aims to provide the basis for
further development of concepts for experimental equipment best suited for the
science needs, including the importance of two complementary detectors and
interaction regions.
  This report consists of three volumes. Volume I is an executive summary of
our findings and developed concepts. In Volume II we describe studies of a wide
range of physics measurements and the emerging requirements on detector
acceptance and performance. Volume III discusses general-purpose detector
concepts and the underlying technologies to meet the physics requirements.
These considerations will form the basis for a world-class experimental program
that aims to increase our understanding of the fundamental structure of all
visible matter
