Influencer marketing is the practice of compensating individuals for posting about a product or service on social media. Influencer marketing is on the rise, and many marketers now plan either to start using influencers or to increase their use of them in their media mixes. Despite such growth, relatively little strategic or academic insight exists that is specific to influencers. In this article, we describe the roots of influencer marketing and the many different types of influencers that now exist. We identify influencers' three functional components: the audience, the endorser, and the social media manager. We then detail for each of these components the different sources of value influencers potentially offer marketers. We draw on relevant academic research to offer advice about how to leverage each component strategically. We close by describing how the interplay of these functional components makes influencers a potentially powerful-and undervalued-marketing tool.