Social media enable increased communication and collaboration among online users, and they have become a ubiquitous part of everyday life for many. The most common social media platforms attract a large number of users: In August 2017, Facebook had about 2.0 billion, YouTube 1.5 billion, WhatsApp 1.2 billion, Instagram 700 million, Twitter 328 million, and LinkedIn 106 million active users.1 With such pervasiveness, people use social media not only in everyday life but also during crisis and emergency events. One of the earliest example of this kind of social media use occurred during the 9/11 attacks in 2001. During these attacks, the Federal Emergency Management Agency (FEMA) and the Red Cross employed web-based technologies to disseminate information to the public and to report the status of the relief efforts externally and internally (Harrald, Egan, & Jefferson, 2002). Additionally, citizens created wikis to gather information about missing persons (Palen & Liu, 2007). Since about 2006, the use of social media in managing crisis events has gained increasing interest among researchers. This area of study is often called crisis informatics. Established by Hagar (2007) and later expanded upon by Palen, Vieweg, Liu, and Hughes (2009), crisis informatics “views emergency response as an expanded social system where information is disseminated within and between official and public channels and entities.” Crisis informatics “is a multidisciplinary field combining computing and social science knowledge of disasters; its central tenet is that people use personal information and communication technology to respond to disaster in creative ways to cope with uncertainty” (Palen & Anderson, 2016). The purpose of this article is to review the crisis informatics research literature, report trends, and offer perspective on the future of this research. We begin with an overview of the many case studies of social media use in emergencies (Section 2). Many crisis informatics studies focus on specific events, such as the 2013 European floods (Reuter, Ludwig, Kaufhold, & Pipek, 2015a), the 2011 London riots (Denef, Bayerl, & Kaptein, 2013), or the 2012 Hurricane Sandy (Hughes, St. Denis, Palen, & Anderson, 2014). We provide a sample of the many different kinds of events that have been studied and summarize trends across these events. Next, we examine the different types of research that can be found in the crisis informatics literature with the aim of helping the reader understand the most common approaches to research in this area (Section 3). We then break down the literature by the different types of interaction studied and derive use patterns (Section 4). Finally, we discuss future directions for this research (Section 5).