One of the oldest social science theories applied to the study of communication, the gatekeeping approach emphasizes the movement of bits of information through channels, with an emphasis on decision points (gates) and decision-makers (gatekeepers). Forces on both sides of a gate can either help or hinder the information’s passage through a channel. The gatekeeping process shapes and produces various images of reality, not only because some bits of information are selected and others rejected, but because communication agents put information together in different ways. In addition, the timing and repetition of information can affect the prominence of events or topics and can influence the probability of future information diffusion. Gatekeeping was originally modeled as a series of linear processes within the mass media, but in the late 20th century the flow of information through the mass and social media began to interact. Information is now understood to flow among journalists, among social media users, and among agents of both types of media. All such communication agents are gatekeepers. In addition, we can study these networked interconnections as one level of analysis, with the supra-gatekeepers (such as Facebook or Twitter) adding their own gatekeeping processes over and beyond those of their own clients of the mass media. In addition to looking at various pairwise relationships between gatekeepers, gatekeeping theory should go beyond to instead consider the entire web of gatekeepers as a whole or system. A system is composed of elements (gatekeepers), interactions (relationships among them), and a goal or function. Multiple functions have been proposed by 20th-century scholars (such as socialization, entertainment, or surveillance) for the mass media, but scholars should now consider the function(s) of the gatekeeping system (mass and social media, as well as supra-gatekeepers) as a whole. Although each type of medium can be analyzed as its own system, such analysis would not facilitate new thinking about the various ways in which these partial systems affect one another and how the whole system functions beyond the simple addition of its parts.