Much research has examined how different patterns of social interaction shape language learners' interactional roles (e.g., collaborative, dominant, passive) in peer-to-peer conversations. However, little or no research has investigated the co-construction of such roles in multiparty, online task-based dialogues within the framework of discursive leadership. For the purpose of this study, discursive leadership is defined as the ability of the interlocutors to (a) shape the discourse via topic introductions and subsequent topic mentions and (b) manage the process of the task through the use of a series of task-oriented speech acts such as directives and assertions. Using a multi-method approach to the computational and quantitative sociolinguistic analysis of online discourse, this study explores the ways in which advanced non-native English speakers (NNESs) differ from native English speakers (NESs) in their attempts to exert discursive leadership in online task-based dialogues. A total of eight groups (four NES and four NNES)--comprised of five to six participants each--participated in a 90-minute online task-based dialogue. The results showed that NNES groups produced shorter discourse and tended to develop a slightly more centralized leadership structure in comparison with NES groups. The results also revealed a significant correlation between NNES participants' discursive leadership values and their conceptual fluency scores derived from the analysis of speakers' formulaic language use (i.e., speech formulas, situation-bound utterances, phrasal verbs, and idioms). More specifically, NNES participants who exhibited a high degree of discursive leadership also tended to have a high degree of formulaic language use, which led group members to perceive those participants as more native-like compared with other group members. Participants' discursive leadership scores also tended to correlate highly with their own judgments of leadership rankings within their groups. The findings also revealed that NNES participants' individual characteristics as well as contextual factors may impact their interactional engagement with the task, which in turn may shape the group's emergent leadership structure. The implications of the study are discussed in relation to task-based language education, collaborative group learning, and interlanguage pragmatics. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]