The James Webb Space Telescope (JWST) is opening a new window of the most distant universe and will unveil the early growth of supermassive black holes (BHs) in the first galaxies.The existence of supermassive massive BHs observed when the universe was younger than one billion years strongly constrains their formation pathway and provides a crucial hint to understand the coevolution between BHs and galaxies. In this talk, I will review the physical mechanisms that promote rapid assembly and growth of seed BHs in early protogalaxies, and discuss how JWST will probe the earliest structure formation in the near future.