This volume covers the field of circular accelerators and related technology for the sub-GeV to multi-GeV energy region from the viewpoint of realization of high performance, i.e., performance and perspectives of operating multi-GeV accelerators, future projects in the multi-GeV energy region, lattice designs and beam dynamics, electron cooling and stochastic cooling, injection and extraction, beam diagnostics, superconducting and normal magnets, magnet power supplies, RF systems, and internal targets. The contributors include leading accelerator physicists from around the world.