Photons, the individual quanta of the light field, are what the science of quantum photonics is dedicatedly investigating. The manipulation and coherent control of photons in quantum photonics enables the exploration of various quantum phenomena of high fundamental interest. In the meantime, due to the fast speed and a lack of the interaction with the environment, photons are now regarded as a promising platform for the emerging quantum information processing (QIP) studies. Therefore, there is a growing number of works on quantum computing, quantum communication, and quantum metrology that are solidly based on the techniques of quantum photonics.