Objective: This study investigated the Diffusion of Innovation (DoI) model in explaining the frequency of adoption and intention to adopt Cattell-Horn-Carroll (CHC) theory by practicing Australian psychologists as a well-validated interpretive model when conducting cognitive assessments. Method: Participants were psychologists with general registration (N = 42-78 depending on the analysis) who completed a survey assessing cognitive assessment practices and perceived innovation characteristics of the CHC model. Results: Few psychologists in the sample were found to be employing CHC in practice, supporting the presence of a theory-practice gap within the cognitive assessment field in Australia. In addition, it was found that the DoI perceptions of compatibility, complexity, and relative advantage were helpful in explaining adoption/non-adoption. Conclusions: Highlighting the compatibility, complexity and relative advantage of the CHC model to psychologists could assist with addressing the theory-practice gap in cognitive assessment in Australia.