Research background: Using enterprise social media (ESM) in the workplace has become an important channel for initiating communication activities for employees in the organization. However, some organizations reported that they did not obtain expected returns from their ESM investments. This outcome may be attributed to employee underutilization of ESM. Thus, exploring how employees use ESM is vital to improving communication efficiency. Research questions: 1. How does ESM support for contextualization affect employees’ dependency relations with ESM? 2. How do dependency relations affect ESM use? Literature review: For professional communicators and other workers, dependency relations can enhance their media use behavior by channeling more useful information. In studying how professional communicators use a medium, researchers indicated that users’ continuance intention rarely occurs without users’ dependency on the medium, thus making media system dependency (MSD) relations critical for media use. Based on the MSD theory, we investigate how ESM support for cognitive and affective contextualization affects employees’ understanding, orientation, and play dependency relations with ESM, and consequently affect work-related and social ESM uses. Methodology: We surveyed 258 employees of a large software development firm in China. Results and conclusions: Our findings suggest that technical and professional communicators who have not yet used ESM in their work may take the following steps: 1. explore ESM and their specific use by employees; 2. manage and control different information sharing among employees on ESM so as to satisfy employees’ different goals; and 3. design and develop different ESM functionalities.