The concept of technology readiness levels was originally introduced by NASA in the 1970ties.

The basic concept is widely adopted by funding programmes, who define the innovation journey as a movement from TRL 1 through TRL 9. 

Funding programmes often target part of the journey and may require that a certain TRL has been reached before allocating funding.

TRL 1: Basic principles observed

TRL 2: Technology concept formulated

TRL 3: Experimental proof of concept

TRL 4: Technology validation in lab

TRL 5: Technology validated in relevant environment

TRL 6: Technology pilot demonstrated in relevant environment

TRL 7: System prototype demonstrated in operational environment

TRL 8: System complete and qualified

TRL 9: Actual system proven in operational environment