Social media are increasingly implemented in work organizations as tools for communication among employees. As these technologies begin to proliferate across the enterprise, it is important that we develop an understanding of how they enable and constrain the communicative activities through which work is accomplished because it is these very dynamics that constitute and perpetuate organizations. We begin by offering a definition of enterprise social media and providing a rough historical account of the various avenues through which these technologies have entered and continue to enter the workplace. We also review areas of research covered by papers in this special issue and papers on enterprise social media published elsewhere to take stock of the current state of out knowledge and to propose directions for future research.  The purpose of this article is to explore, at this early date, what consequences -positive and negative -social media used for communication and interaction within the workplace may have for those socio-technical systems we call organizations. Enterprise social media (a term we define and explain below) are distinct from traditional communication technologies often used in today's organizations because those who use them can see conversations occurring between others in the organization who are not their communication partners and can distinguish social and work related connections among them. In other words, rather than functioning as a channel through which communication travels, enterprise social media operate as a platform upon which social interaction occurs. Because this platform is digital, in contrast to the physical platforms of offices, conference rooms, and hallways that have traditionally been the stages on which most workplace communication is played out, anyone in the organization can participate at any time from any place. Due to the dramatic changes in social interaction that enterprise social media portend, it is no surprise that industry analysts and the business press predict unprecedented transformations in the way organizations that adopt them will operate in the coming decades. As these new technologies begin to proliferate across organizations, it is important that we develop an understanding of how they enable and constrain the communicative activities through which work is accomplished because it is these very dynamics that constitute and perpetuate organizations. We begin by defining enterprise social media and providing a rough historical account of the various avenues through which these technologies have entered and continue to enter the workplace. We also review areas of research covered by papers in this special issue and papers on 2 enterprise social media published elsewhere to take stock of the current state of our knowledge and to propose directions for future research. In the short time in which they have been present in organizational contexts, social media seem to have been used in two primary ways. The first, and more commonly studied, way is for organizational communication with external parties, such as customers, vendors, and the public at large. Most organizations that use social media to communicate with external parties have a multipronged strategy that crosses various platforms (Piskorski, 2011) . For example, they maintain pages on popular public social networking sites like Facebook and MySpace, and they broadcast messages on micro-blogging sites such as Twitter. Their employees also sometimes write blog posts on news websites and, occasionally, they host social tagging sties. Communication on these sites is faced externally. The second and, heretofore, less commonly studied way in which organizations have employed social media is for internal communication and social interaction within the enterprise. It is these internal social media platforms that occupy our attention in this special issue. Unlike external uses of social media that cross many public platforms, most organizations implement an integrated social media platform for internal communications that contains several functions (McAfee, 2009 ). For example, most internal social media platforms mimic in look, feel, and functionality popular social networking sites such as Facebook. But embedded within the platform one can often find blogs and wikis, as well as features through which social tagging and document sharing can happen. Thus, when talking about social technologies used for communication within the enterprise, it makes less sense to distinguish between tools such as social networking, micro-blogging, and social tagging, 3 and more sense to treat these individual tools as part of an integrated enterprise social media platform. For this reason, we define enterprise social media (hereafter, ESM) as: Web-based platforms that allow workers to (1) communicate messages with specific coworkers or broadcast messages to everyone in the organization, (2) articulate a list of coworkers with whom they share a connection, (3) Consequently, people can interact with a communication, rather than the communicator, long after the conversation is over. Persistence of communicative actions provides a direct pathway to an organization's memory (Walsh & Ungson, 1991) . The fact that the messages people send to one another, the networks they articulate, the text they produce, and the files they post are visible to everyone in the organization and persist in their original form over time means that others throughout the enterprise who were not involved in the original communication have the opportunity to learn from and contribute to it. Perhaps the most important effect of visibility and persistence is that they enable employees to learn from the 6 communications of others. There are at least two kinds of knowledge people can learn by participating in ESM: Instrumental knowledge and Metaknowledge. Instrumental knowledge is knowledge about how to do something. Direct exposure to instrumental knowledge has been shown to be an important mode of social learning in organizations (Huber, 1991) . But research shows that direct exposure is often impeded because people simply do not know what knowledge exists out there to be learned, or where that knowledge lies (Lave and Wenger, 1991). They do not have an awareness of what knowledge exists in the organization because it has been communicated in a visible format and/or it does not persist over time. Metaknowledge is knowledge about what and whom other people in the organization know. Metaknowledge is important for the functioning of organizations because it is an important antecedent to the transfer of instrumental knowledge (Ren & Argote, 2011). As one example of a way in which visibility and persistence afforded by ESM may help new employees engage in the social learning necessary to develop metaknowledge quickly, imagine a new employee to marketing who needs to extract data on consumer purchasing behavior from the company's datacenter. As a new employee, she might be aware that the datacenter has this information, but not have insight about who to contact to access it. If, when reviewing content on the social media platform, this employee sees that a colleague in marketing has talked with someone in the datacenter, she begins to develop metaknowledge. Because she knows that the colleague in marketing knows someone at the datacenter, she can ask the colleague in marketing if this is the correct person from whom to obtain the data she needs. Were the communication between the colleague in marketing and the person in the datacenter to happen through a channel that did not afford visibility and persistence, like the telephone, the new employee would not have been able to easily and quickly develop the metaknowledge necessary to obtain the information with which to complete her assignment. 7 The emergence of ESM has typically followed one of three primary paths into organizational contexts: (1) use of publicly available sites like Facebook, Google+, and Twitter, (2) private implementations of open source or proprietary software, either installed on a company's own servers or acquired as a hosted (cloud-based) software service, or (3) in-house proprietary solutions, often built as prototypes by software vendors for later incorporation into commercial offerings. We elaborate on each of these paths below. Although many organizations now routinely use publicly available social networking and microblogging sites for customer-facing innovation, marketing and after sales service purposes (Kaplan and Haenlein, 2010) , in the years before popular sites allowed business pages, employees often independently joined and interacted with coworkers on public social media. In many cases, these experiences predated the establishment of internal-only social media applications.  The literature on ESM documents a number of examples of proprietary, custom-built systems, usually developed by computer (both hardware and software) and information technology companies that have vested interests in understanding how organizations might employ such new computer-based applications. These types of companies not only stand to benefit from the potential for increased productivity of their own knowledge workers, but also have an obvious interest in the potential that ESM can have for their product mix. Their prototypes have been used to support research that informs internal production systems and future commercial products, or otherwise supports client needs. Two custom ESM examples that have been the subject of several papers are the Beehive system developed at IBM Steinfield et al, 2009 ) and the Watercooler system developed at HP (Brzozowski, 2009). The Beehive system, launched in mid 2007, garnered over 30,000 users before the end of the year . It encompassed many of the features found on public sites like Facebook, but was restricted to IBM employees. Employees reported connecting with both close colleagues and "weak ties", but reported greater content sharing with their more distant connections, leading DiMicco and colleagues to conclude that the site had helped to form new ties and strengthen weak tie relationships within the company. A later study of Beehive use by Steinfield et al (2009) similarly found that usage of the site was associated with a number of social capital benefits such as increased access to new people and expertise, as well as perceptions of belonging to a larger community. At HP, the WaterCooler system essentially was developed to bring together the feeds from the many separate social media systems that were proliferating in the company (Brzozowski, 2009) . The system indexed these feeds by novelty, popularity, author, and topic, and enabled users to filter posts. Based on a survey, as well as a network study of commenting behavior that compared internal blog reading by WaterCooler users versus non-users, the author concludes that the system enhanced employees' access to new people and expertise outside their local units. WaterCooler readers were more likely to access blogs from outside their local unit than other readers. These research prototypes often have a limited lifespan, and the lessons learned from such prototypes are used to inform other internal systems and commercial products. For example, Beehive, which at its height had over 65,000 members, was discontinued in 2011 but had many of its features incorporated into a new internal site called SocialBlue. Today IBM offers a product called Connections that incorporates features from these earlier prototypes. Microsoft also benefited from its early experiences with various from social media, ultimately incorporating many social media features into its commercial Sharepoint offering. Prospects for the Study of Enterprise Social Media Our understanding of the role that ESM play in organizational life is in its infancy. To date, most studies of ESM have been conducted by scholars within the computer-supported cooperative work (CSCW) and human computer-interaction (HCI) communities. That these two communities would be the forbearers of research on ESM is understandable, given that many of the authors of papers from these areas were themselves creators of specific ESM applications (e.g. the homegrown applications we discussed in the previous section), or worked in organizations in which these Given these trends, the time seems ripe for researchers to examine how ESM are implicated in various processes that occur within organizations. Specifically, this special issue seeks to provide an initial examination of how the affordances enacted by ESM use may reinforce, alter, or dramatically change how the people carry out important organizational processes. To lay the groundwork for such an endeavor, we have reviewed the literature on ESM use published in the disciplines mentioned above to identify various ways that researchers have characterized ESM so far, and to uncover some of the organizational processes with which ESM use seem to be related. Below, we present three broad metaphors for describing the role that social media play within organizations: ESM as a Leaky Pipe, ESM as an Echo Chamber, and ESM as a Social 12 Lubricant. As described above, the visibility and persistence of communicative behavior afforded by ESM use provides new and enhanced opportunities for social learning within organizations. Our review of the literature suggests that these opportunities for social learning have implications for at least four common processes within organizations: Social Capital Formation, Boundary Work, Attention, and Analytics. Below, we review each of these metaphors and discuss, in turn, how viewing each of these four processes from the vantage point provided by the particular metaphor bring potential advantages and disadvantages related to each of the processes into focus, which may provide direction for future research. Table 1 summarizes our discussion. In working through the logic of Table 1 , we also discuss the stances that the authors of the various papers in this special issue take on these processes. This special issue is comprised of five excellent papers. Fulk and Yuan discuss how the affordances of ESM can help reduce three challenges in sharing organizational knowledge: How people locate expertise, their motivation to share knowledge and their ability to capitalize on their social connections. To do so, they draw on transactive memory, public goods, and social capital theories to show how ESM function as hybrids of communal and connective goods within the organization. Majchrzak, Faraj, Kane, and Azad also focus on organizational knowledge sharing. They theorize four ESM affordances -metavoicing, triggered attending, network-informed associating, and generative role-taking -that represent different ways to engage in the publicly visible knowledge conversations enabled by social media use. These four affordances overlap in some ways and depart in others from the four ESMaffordances of visibility, persistence, editability, and association -outlined earlier by Treem and Leonardi (2012) . Majchrzak and her colleagues argue that ESM use creates the opportunity to turn organization-wide knowledge sharing from a centralized process into a continuous conversation of 13 strangers. Pike, Bateman, and Butler confront the tensions of information quality and availability faced by hiring managers within organizations. They find that the affordances of ESM create an abundance of information for organizational decision-making, but provide no means by which to interpret its quality. Consequently, managers have to engage in several strategies to reduce tensions of accessibility, contextual cues, and intrinsic interest inherent in the information ESM provide them. Vaast and Kaganer focus on governance issues in ESM use. Specifically, they examine how organizations craft policies to respond to the affordances provided by ESM and they consider how these policies, alongside the ESM affordances, might shape people's use of these tools in the workplace. Finally, Gibbs, Rozaidi, and Eisenberg provided a much needed critical evaluation of ESM use, arguing that much of the emerging literature on social media in the workplace use is characterized by an "ideology of openness," which assumes ESM use will increase knowledge sharing in organizations, and that open communication is effective and desirable. Their study of ESM use in a geographically distributed organization shows how users limit as well as share knowledge through social media, and the productive role of tensions in enabling them to attend to multiple goals. One common metaphor that has implicitly guided many studies of social media use within organizations up to this point is that ESM are leaky pipes for organizational communication. In using the metaphor of a leaky pipe we mean to suggest that the directionality of a particular communication
Looking at the intersection of social media and communication research, REF state, "Researchers in the field of communication have focused a good deal on social media use among youth and college students, but they have not considered how such tools are used within organizational contexts" (p. 6).
1 Enterprise Social Media: Definition, History, and Prospects for the Study of Social Technologies in Organizations
J. Computer-Mediated Communication
J. Computer-Mediated Communication
Sociology Computer Science