This document provides a literature review on social media advertising strategies employed by fast fashion brands like H&M and Zara and their impact on customer purchase intentions and brand loyalty. It identifies several theories that explain how social media advertising can influence consumer behavior, such as the 4C framework and Hierarchy of Effects model. Popular social media strategies used by fast fashion brands, including display ads, photo and video posting, are also examined. While social media advertising is found to be generally more effective than traditional methods, more research is still needed to understand its effects according to different theories. The review informs the study's methodology to analyze the link between H&M's and Zara's social media strategies and customer outcomes in the UK.