# Technology Readiness Levels (TRLs) in the Era of Co-Creation
## 1 Introduction  
Technology readiness levels (TRLs) is a methodological tool that emerged to assess the maturity of new technology. The approach was first developed and standardized by NASA [1]; the initial intention was to provide a disciplined way to differentiate between technology readiness levels. The original definition of TRL was a scale from level 1, corresponding to the formulation of a new concept, up to level 7, which ascertained that the system had been successfully demonstrated in a real environment [1]. Although initially used within NASA and aimed at securing a common language between research and operational personnel, the TRL approach has now extended well beyond NASA and the aerospace industry and has been widely adopted across research and industry. In the process, it has also expanded to nine levels [2]; indeed, this nine-level scale corresponds to the formulation currently in use worldwide. Numerous entities beyond NASA are using the TRL system, and [PERSON] [2] provides evidence of a global adoption, even though some users may opt for some slight modifications or more extensive documentation on the meaning of every single readiness level. One example is the European Space Agency's Handbook [3], which defines each level by numerous standards that a technology must meet to be categorized at the particular level. Interestingly, the TRL approach is widely used as a mechanism to classify innovation. Innovation is strongly related to the development and implementation of new technologies, and TRL can be a useful tool for assessing the progress and potential of these technologies. For example, investors may use TRL to evaluate the potential risks and rewards of investing in a particular technology, while policymakers may use TRL to assess the feasibility of implementing a new technology in a particular sector. Thus, in Horizon Europe, the EU's program for research and innovation, proposers and contractors are typically required to position their research and development planagainst this ladder and explain what both the starting TRL and target TRL are. Figure 1, below, illustrates the nine levels of the EC's TRL ladder and provides a short description of each level. The nine-level model was also implemented by the US Department of Energy (DoE) with small variations in some levels [4]. In other cases, the TRL was modified to assess the readiness not only of technology but of the process of incremental innovation [5], and the innovation readiness level was defined. Two more levels, level 10 and level 11, have also been recommended in the literature [6; 7], and this is something which demonstrates the constantly evolving nature of technology maturity classification towards an always greater resolution. However, in the following discussion, we will restrict ourselves to the nine levels shown in Figure 1, as the authors consider levels 10 and 11, in which technology is continuously improved or applied to new contexts, to be beyond TRL 9. Levels 10 and 11 have not been standardized or widely recognized in the TRL framework. Therefore, limiting a conversation on TRL to the first nine levels is practical because it covers the entire spectrum of technological development and represents a widely accepted framework in the scientific and engineering communities. While TRLs offer valuable guidance, they have certain limitations that may affect their ability to fully reflect the readiness of innovations and suggest the next natural steps for ascending the maturity ladder. In the discussion below, we will present an empirical case which provides evidence that the TRL approach cannot always provide guidance as regards the next step up the innovation ladder. We will discuss why this has been the case and what the explicit limitations and eventual workarounds have been found to be. We will also attempt to generalize and delineate the particular features that render the TRL approach insufficient in specific settings.