This master thesis investigates how representations of science and professional expertise are manifested in advertisements for health, beauty and wellness products, and which ways science and professional expertise are utilized in arguments to sell these products. Through a multimodal textual analysis, four video advertisements distributed to Norwegian audiences between 2015 and 2017 are investigated. The first part of the analysis shows that science and professional expertise is typically represented in a stereotypic manner, drawing largely on visual cues and the use of discipline-specific terminology to convey an institutional context associated with knowledge-based authority. The second part of the analysis shows that science and professional expertise are used as selling arguments in a number of ways. I argue that that most important role of science and professional expertise in the argumentation is the use of them as a contextual frame and stereotype with generally positive connotations. Science and professional expertise are portrayed as knowledge-based authorities that are relatively closed off to the public, and as able to deal with problems that are too complex for regular people to fully understand. The message is therefore that we are expected to trust science and professional expertise rather blindly as bearers of truth, even when they are in fact being used as a means to sell a commercial product