<p>Photonic quantum technologies are now progressing from demonstrations of fundamental phenomena to systems of sufficient scale and quality to enable practical applications with quantum advantage in communications, computation and metrology. Here we review recent advances in quantum optics that have led to the emergence of such scalable quantum technologies, and outline the road ahead to more general applications with greater potential impact. We first focus on the components that support various photonic quantum applications, including quantum light sources, linear-optical networks and detectors. We go on to discuss recent experimental demonstrations of quantum communication, quantum computation and simulation, and quantum metrology using photons. Finally, an overview is provided on the manner in which photons fit within both the opportunities and challenges of implementing space-to-ground quantum internet, universal quantum computing and quantum precision measurement.</p>