Metrology for Testing the Implementation Security of Quantum Key Distribution (MeTISQ) Data is one of the world’s most valuable commodities – affecting every person, every company, every government, everywhere. Never before has it been so important to store and communicate this data in a secure manner. Most of the world’s cybersecurity infrastructure is based on the exchange and use of digital cryptographic keys. This has been very effective so far, however advances in quantum computing have dramatically raised the threat to this infrastructure. MeTISQ aims to develop robust, SI-traceable measurements, at the single-photon level, to characterise quantum key distribution (QKD) systems (assembled transmitter and receiver modules) and technologies aligned with the actual standardisation development work of the ETSI Industry Specification Group on QKD. The expertise gained in developing the measurements for practical QKD implementation security will be used to lead the drafting of measurement specifications and standards by the European Telecommunications Standards Institute Industry Specification Group on QKD (ETSI ISG-QKD), the principal stakeholder of this project.