Technology Readiness Levels grade a technology’s maturity from TRL 1 (basic principles observed) to TRL 9 (system proven in operation). NASA developed the scale for spaceflight hardware; the European Commission adopted it across Horizon programs, an ISO standard (16290) codified it for space systems, and deeptech investors and grant agencies now use it as a shared shorthand for “how far from the real world is this”.
The bands that matter in practice: TRL 1-3 is research (principles, concepts, first proof of concept); TRL 4-6 is the lab-to-prototype climb where most deeptech startups live and most deeptech funding concentrates; TRL 7-9 is demonstration to deployment. Each transition is a derisking event, and the expensive ones are rarely where outsiders expect: the integration steps (TRL 5-6), where subsystems that each worked in isolation must work together in a representative environment, routinely consume more capital and calendar than the original science.
Used honestly, TRL is a communication device, not a vanity metric: state the system-level TRL, show the per-subsystem breakdown, and attach evidence to the claimed level (what was demonstrated, in what environment, witnessed how). That single table preempts the most common technical diligence dispute and signals that the team knows the difference between a result and a product.