This catalog is maintained by DocNow which responds to the public's use of social media for chronicling historically significant events as well as demand from scholars, students, and archivists, among others, seeking a user-friendly means of collecting and preserving this type of digital content. DocNow has a strong commitment to prioritizing ethical practices when working with social media content, especially in terms of collection and long-term preservation. This commitment extends to Twitter's notion of honoring user intent and the rights of content creators. The project is a collaborative effort among the University of Maryland, University of California at Riverside, and Washington University in St. Louis. We are extremely grateful for funding from the Andrew W. Mellon Foundation.