The study aims to contribute to the research on service quality, analyzing almost 30 years of research on the Gaps Model proposed by Parasuraman, Zeithaml and Berry in the 1980s. A literature review has been conducted from 1985 to 2013 with the purpose of underlining the model evolution and its criticisms. Major international academic databases have been consulted. On this basis the paper summarizes some theoretical-conceptual and methodological-operational critical aspects identified by scholars who analyzed and applied the model and the scale. Despite that, the Gaps Model and the SERVQUAL scale are still the most used instruments to study service quality in marketing literature. The analysis allows to identify interesting points for future research on the topic of service quality. The conceptual framework presented in the paper does not include any empirical research that could be eventually implemented to validate the findings.