SuperKEKB, a 7 GeV electron - 4 GeV positron double-ring collider, is constructed by upgrading KEKB in order to seek new physics beyond the Standard Model. The design luminosity of SuperKEKB is 8 x 10^35 /cm^2 /s - 40 times higher than that achieved by KEKB. The greater part of the gain comes from significantly decreasing the beam sizes at the interaction point based on the nanobeam collision scheme; the design beam currents in both rings are double those achieved in KEKB. Large-scale construction to upgrade both the collider rings and the injector was conducted, and beam commissioning without the Belle II detector and final-focus magnets was successfully carried out from February to June in 2016. Subsequently, renovation of the interaction region, including the installation of the final-focus magnets and Belle II, and construction in the final stage of a new positron damping ring were conducted. Having completed the interaction region, beam collision tuning is scheduled from March till July in 2018. This paper reviews the design, construction, and beam commissioning of SuperKEKB.

Accepted by Nuclear Instruments and Method in Physics Research A (NIM A), latex(hyperref), one column, 21 pages, 17 figures, 3 tables. Fig.5 and Table.1 were updated