Due to the severe short-channel effects, silicon-based transistors cannot work well when the gate length is shorter than 10 nm. Moore’s law is at risk of failure. Compared to bulk semiconductor materials, two-dimensional (2D) materials own better electrostatic features and higher carrier mobilities. To describe the transport properties of transistors at the nanometer scale, the first-principles quantum transport simulation based on density functional theory coupled with non-equilibrium Green’s function method is the most precise theoretical tool. The device performances of ideal 2D transistors are predicted to surpass those of silicon-based transistors based on the first-principles quantum transport simulation, which can meet the International Technology Roadmap for Semiconductors (ITRS) and International Roadmap for Device and Systems (IRDS) requirements for the next decade and extend Moore’s law to sub-10 nm gate lengths . We review dramatic experimental breakthroughs on 2D transistors in the recent two years, including shrinking the gate length to the Angstrom scale, descending the electrode contact resistance to the quantum limit, and fabricating high-quality and ultrathin dielectric. When Ohmic contacts and high-quality ultrathin dielectric layers are simultaneously realized, theoretically predicted superior performances beyond silicon are observed in 10-nmgate InSe transistors experimentally.