Continuous-Variable Quantum Key Distribution is an alternative to the usual discrete variable quantum key distribution schemes, such as BB84, based on quantum states of light. Optical quantum states are defined in an infinite dimensional Hilbert space hence the "continuous" prefix. Compared to DV-QKD, CVQKD has several advantages such as being compatible with existing telecommunications equipment as one only needs to modulate coherent states of light and perform homodyne/heterodyne detections, but suffers from a lower range, and security proofs are somewhat harder.