In-fiber integrated optics is the use of quartz fiber as the substrate material, by miniaturizing and integrating various optical paths or optical components into an optical fiber, to build a functional optical device or component, or through the integration of several functional optical devices, to achieve the integration of micro-optical systems on the optical fiber. In-fiber integrated optics is expected to become a new branch of photonics integration. This integration technology can easily control and manipulate the light wave in a single fiber, provides a flexible and convenient platform for the research of integrated optics, and provides an effective method and means for the integration of microphotonics devices and systems. Through a series of integration examples, this chapter summarizes the main ideas and key technologies of optical device integration and micro-optical system integration in optical fiber and provides some basis for further development in this direction.