Twisted light, an unbounded set of helical spatial modes carrying orbital angular momentum (OAM), offers not only fundamental new insights into structured light-matter interactions, but also a new degree of freedom to boost optical and quantum information capacity. However, current OAM experiments still rely on bulky, expensive, and slow-response diffractive or refractive optical elements, hindering today's OAM systems to be largely deployed. In the last decade, nanophotonics has transformed the photonic design and unveiled a diverse range of compact and multifunctional nanophotonic devices harnessing the generation and detection of OAM modes. We summarize recent metasurface devices developed for OAM generation in both real and momentum space, presenting design principle and exemplary devices. Moreover, we summarize recent development of whispering gallery mode-based passive and tunable micro-cavities, capable of extracting degenerate OAM modes for on-chip vortex emission and lasing. In addition, we discuss the design principle of different plasmonic devices and photodetectors recently developed for on-chip OAM detection. We further discuss current challenges faced by the nanophotonic field for twisted light manipulation and future advances to meet these challenges. We believe twisted light manipulation in nanophotonics will continue to make significant impact on future development of ultracompact, ultrahigh-capacity, and ultrahigh-speed OAM systems-on-a-chip.