High-energy particle colliders have been the primary facilities of discoveries in fundamental particle physics in the past few decades. After the discovery of the Higgs boson in 2012, the near term priorities of high-energy physics are precision measurement of the Higgs boson and full exploitation of the physics potential of the Large Hadron Collider (LHC) through its high-luminosity upgrade (HL-LHC). A number of the next generation collider facilities have been proposed and are currently under consideration for the medium and far future of accelerator-based high-energy physics. The most promising proposals include linear e+ e- colliders in Japan (ILC), CERN (CLIC), circular lepton or hadron colliders in Europe (FCC-ee and FCC-pp) and China (CEPC/SPPC). In this talk, I will review the physics potential of these future colliders, with special focus on the CEPC, and discuss the challenges and R&D of detector concepts in order to meet the physics requirement. I will summarize this talk with keynote messages I learned from the January IAS High Energy Physics program in Hong Kong.