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Quantum key distribution (QKD)^, has the potential to enable secure communication and information transfer. In the laboratory, the feasibility of point-to-point QKD is evident from the early proof-of-concept demonstration in the laboratory over 32 centimetres; this distance was later extended to the 100-kilometre scale^, with decoy-state QKD and more recently to the 500-kilometre scale^{, , –} with measurement-device-independent QKD. Several small-scale QKD networks have also been tested outside the laboratory^{, , –}. However, a global QKD network requires a practically (not just theoretically) secure and reliable QKD network that can be used by a large number of users distributed over a wide area. Quantum repeaters^, could in principle provide a viable option for such a global network, but they cannot be deployed using current technology. Here we demonstrate an integrated space-to-ground quantum communication …