This book makes simultaneous contributions to the theory of metadiscourse (commentary on the ongoing discourse), corpus-based methods of studying such phenomena, and our knowledge of metadiscourse use in written English. After comprehensively reviewing previous research, it introduces a more rigorous and empirical approach to metadiscourse studies. Ädel presents a new model of metadiscourse based on Jakobson’s functions of language, and other conceptual tools, including explicit features for defining metadiscourse, a taxonomy of the functions it serves, and maps of the boundaries between it and related phenomena. A large-scale study of writing by L1 and L2 university students is presented, in which the L2 speakers’ overuse of metadiscourse strongly marks them as lacking in communicative competence.