The widespread use of social media as a marketing tool during the last decade has been responsible for attracting a significant volume of academic research, which, however, can be described as highly fragmented to yield clear directions and insights. We systematically synthesize and critically evaluate extant knowledge of social media marketing extracted from 418 articles published during the period 2009–2021. In doing so, we use an organizing framework focusing on five key areas of social media marketing research, namely, social media as a promotion and selling outlet, social media as a communication and branding channel, social media as a monitoring and intelligence source, social media as a customer relationship management and value cocreation platform, and social media as a general marketing and strategic tool. Within each of these areas, we provide important theoretical, methodological, and thematic insights, as well as future research directions. We also offer useful managerial implications derived from the articles reviewed.