As the only quantum information carrier at atmospheric pressure and temperature, photons play a versatile role in the quantum information ecosystem. Recent progress in fabricating high-quality-factor microresonators has enabled unprecedented control of photons through nonlinear optical interactions. In this talk, I will focus on the precision-metrology aspect of quantum photonics. I will discuss the on-chip generation of several optical sources for metrology, including squeezed vacuum, optical parametric oscillators, and Kerr frequency combs. I will also discuss synchronization of different optical sources to enable new functionalities, such as ultra-stable microwave generation. I will further discuss the prospect of combining these techniques with novel squeezing to achieve optical linewidths beyond the vacuum-noise limit. Finally, I will briefly discuss other microresonator-based applications, including quantum frequency conversion and spatial light modulation.