Optical quantum metrology encompasses the generation, detection, characterization, and verification of quantum states of light, including the use of quantum entanglement to enhance sensitivity compared to classical methods. The project develops cutting-edge single-photon sources and uses state-of-the-art (photon-number-resolving) single-photon detectors to investigate fundamental aspects of optical quantum metrology. Further, the project focusses on the implementation of newly developed measurement protocols and characterization tools for single-photon sources, detectors, and components. These tools and protocols are used for applications such as entanglement distribution in quantum networks, synchronization of distant quantum network nodes, quantum component characterization and quantum-enhanced measurements using exotic and non-Gaussian quantum states of light.