Objective
In this study, we examined the effectiveness of the ItFits-toolkit and answered the following research question: does the use of the ItFits-toolkit lead to better outcomes than implementation-as-usual (IAU) in implementing iCBT services in routine mental health care? Implementation effectiveness was defined as the extent to which the iCBT services were regarded as being a normal part of mental health care practice by service providers. We hypothesized that ItFits-toolkit use would be associated with increased normalization of iCBT services into practice. Parallel to this effectiveness study, an in-depth qualitative process evaluation was conducted, focusing on engagement, embedding, and integration of the ItFits-toolkit by implementers [