The Technology Readiness Levels (TRLs), initially adopted by NASA, were introduced in ESA in order to enable discipline-independent assessments of the maturity of a particular technology and the consistent comparison of maturity between different types of technology, all in the context of a specific system, application and operational environment.
The concept became a well-established standard, not only in ESA and NASA, but also in many Agencies and Industry around the world. However, although the implementation of the concept by all these actors was somewhat similar, different definitions or interpretations were used.
To ensure that exchange of information on TRL was completely meaningful around the world ESA, as part of ECSS, proposed to ISO a global harmonization of the TRL definition in 2009. The ISO TRL Work Group (WG) successfully converged to a unified international scale endorsed by all major space actors, with a common understanding of the associated definitions, which lead to the creation of an ISO TRL WG to which ESA and ECSS have actively contributed by providing WG members.
The activity of this WG ended in the publication, in 2013, of the standard ISO 16290 “Definition of Technology Readiness Levels (TRLs) and their criteria of assessment”, and today the ISO TRL scale is becoming a standard in the space sector.
Source: ISO TRL document 16290.
Further info also available via the ECSS website - document ECSS-E-HB-11A (registration is required).