Objective: The current study systematically reviews evidence for a causal chain model suggested by Miller and Rose to account for the efficacy of Motivational Interviewing (MI). Method: Literature searches were conducted to identify studies delivering MI in an individual format to treat various problem areas. Results: Thirty-seven studies met inclusion criteria. The results suggest that when clinicians utilise MI consistent behaviours, clients are more likely to express language in favour of change. Furthermore, this client language was consistently related to positive client outcome across studies. Conclusions: While the results support some parts of the Miller and Rose model, additional research is needed to confirm the findings in diverse populations. Understanding the mechanisms of MI's effectiveness may maximise the implementation of MI, potentially contributing to better client outcomes.