This paper focuses on the pervasive phenomenon of metadiscourse, or reflexivity in language, looking at argumentative essay writing by university students. It presents a study of three varieties of English, using two corpora of native-speaker writing (British and American) and one corpus of advanced learner writing (L1 Swedish). Considerable differences are shown to exist in the use of metadiscourse, not just between the learners and the native speakers, but also between the British and American writers. The differences are evident both in general frequencies across corpora and in the functions the metadiscourse serves. Four factors are identified as potentially accounting for the variation found: genre comparability, cultural conventions, register awareness and general learner strategies.