If you have read a Horizon Europe call document, you have almost certainly encountered the acronym TRL — followed by a number. TRL 3. TRL 6. TRL 7 to 9. These references appear throughout call topics, expected outcomes, and eligibility conditions, and they carry real consequences for whether your project fits a given call.
Yet for many organisations — particularly those engaging with EU funding for the first time — what TRL actually means, how it is assessed, and how to use it correctly in a proposal remains unclear.
This article explains the TRL scale, what each level means in practice, and how the Commission uses it to define the scope and ambition of Horizon Europe calls.
What TRL stands for
TRL stands for Technology Readiness Level. It is a standardised scale, originally developed by NASA and widely adopted across research and innovation policy, that measures how mature a technology is — from initial concept through to fully operational deployment.
The scale runs from TRL 1 to TRL 9. The lower the number, the earlier the stage of development. The higher the number, the closer the technology is to real-world deployment.
In Horizon Europe, TRL is used to define what stage of development a project is expected to start from, and what stage it should reach by the end.
Note: A call that specifies “TRL 4 to 6” is looking for projects that take a technology from proof of concept to prototype validation. A call that specifies “TRL 6 to 8” is looking for projects that take a validated prototype to a pre-commercial product ready for market introduction.
The nine levels explained
TRL 1 — Basic principles observed
The very beginning of the research process. Scientific principles underlying the technology have been identified, but no practical application has been defined. This is fundamental research at its most exploratory.
TRL 2 — Technology concept formulated
The basic principles are applied to a specific concept. The potential application is identified, but experimental proof has not yet been produced.
TRL 3 — Experimental proof of concept
Active research and early development begins. Key functions have been tested analytically or experimentally, and early results support the concept’s viability. This is the stage at which many academic research projects operate.
TRL 4 — Technology validated in lab
The technology has been validated in a laboratory environment. The basic components have been tested together and work as expected under controlled conditions.
TRL 5 — Technology validated in relevant environment
The technology has been tested in an environment that resembles its intended real-world use — not just in a lab. Performance is more representative, and critical functions have been demonstrated.
TRL 6 — Technology demonstrated in relevant environment
A prototype or representative model has been demonstrated in a relevant environment. This is a significant milestone — it represents the transition from development to demonstration.
TRL 7 — System prototype demonstration in operational environment
The technology has been tested in the conditions it will actually face when deployed. This goes beyond demonstration — it is about proving that the system works operationally, not just technically.
TRL 8 — System complete and qualified
The technology is complete and has been tested to the point of qualification for its intended application. This is the stage immediately before commercial deployment.
TRL 9 — Actual system proven in operational environment
The technology is fully operational and proven in real-world conditions. It is ready for, or already in, commercial deployment.
How TRL is used in Horizon Europe calls
The Commission uses TRL references in call documents in several distinct ways:
Defining the starting point. A call may specify a minimum starting TRL — for example, “proposals must address technologies at TRL 3 or above.” This is an eligibility or relevance condition: projects proposing to work at TRL 1–2 would not fit the call’s scope.
Defining the target. A call may specify what TRL the funded projects are expected to reach by the end. “Expected to reach TRL 6 by project end” defines both the ambition and the evaluation benchmark for the project’s outputs.
Defining the range. Many calls specify a range — “TRL 4 to 6” or “TRL 5 to 8” — indicating the expected starting and ending points. This communicates the type of activity the call is funding: is it development, demonstration, or something closer to market deployment?
Differentiating between action types. The TRL range expected is directly related to the type of action being funded. Research and Innovation Actions (RIAs) typically operate at lower TRLs (1–5). Innovation Actions (IAs) operate at higher TRLs (5–8). This distinction matters for how proposals are written and evaluated — more on this in the next article.
How to use TRL correctly in a proposal
Many applicants make one of two mistakes with TRL: they claim too high a starting TRL to appear more advanced, or they claim too low a target TRL to appear more conservative and achievable.
Both approaches backfire.
Evaluators are experts in their field. A proposal that claims TRL 5 for a technology that is clearly at TRL 3 will be identified and scored down for lack of credibility. A proposal that targets only TRL 5 in a call expecting TRL 7 will be seen as insufficiently ambitious.
The correct approach is to assess your technology honestly, against the definitions above, and position the proposal accurately. If the fit with a particular TRL range is not strong, that is usually a signal that the call is not the right one for this project — not that the TRL should be adjusted to match.
When describing TRL in a proposal, be specific. Do not simply state “we are at TRL 4.” Explain what has been tested, in what environment, with what results, and why that constitutes TRL 4 rather than 3 or 5. Evaluators expect evidence, not assertion.
How Kronis supports TRL-aware project management
Understanding TRL is relevant not just at the proposal stage, but throughout project execution. Horizon Europe projects are evaluated at each reporting period against the progress claimed — and if a project commits to reaching TRL 6 by month 24, that commitment needs to be tracked and evidenced.
Kronis PMO allows teams to structure their work plan around the technical milestones — including TRL progression — defined in the Grant Agreement. Progress against those milestones is tracked continuously, so that when reporting time arrives, the evidence of TRL advancement is already in the system.
Final thoughts
The TRL scale is not bureaucratic jargon. It is a precise communication tool that tells evaluators, Project Officers, and reviewers exactly what stage of development a technology is at, and what progress is expected. Used correctly, it strengthens a proposal’s credibility and sharpens the project’s objectives. Used incorrectly, it is one of the clearest signals to an evaluator that the applicant does not fully understand the call — or their own technology.
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