The development of the Internet has caused fundamental changes in many sectors and has also great impacts in the field of marketing. One of these significant changes has emerged with influencer marketing, especially with the increase in the effectiveness of social media platforms. Influencer marketing, especially influencers on social media, influences their followers and contributes to increase a brand's awareness to a wider audience and increasing its sales. One of the biggest reasons why this concept has become increasingly important is that consumers trust influencers in social media more than traditional marketing channels and are more eager to buy the products and services influencers recommend. Influencer marketing has become more widespread, especially with the Covid-19 pandemic, and has increased its popularity in digital marketing. This chapter reviews the studies which primarily focused on the role of influencers in purchasing decisions and gives suggestions for future research.