This study presents a corpus-based investigation of how Arab students of English use modality in academic writing. Although the primary focus of the study is on the writing of Arab L2 learners, regular comparisons have been conducted with native-speakers' writing with the aim of delineating the areas of similarities and differences between the two groups (leaners and native speakers). Furthermore, in an attempt to check whether the features characterizing the use of modality in Arab L2 academic writing is part of a general tendency or an idiosyncratic creation that exclusively applies to Arab students of English, results have been frequently checked against some other relevant studies. The study reveals a gap between native speakers and learners in terms of the frequency count of the modals used. Findings also show that many of the modality features used in the learner corpus reflect a general tendency on the part of most L2 learners. Yet, some other features, including the overuse of 'must', 'can' and 'should' and the underuse of the epistemic modals 'may', 'might', 'would', and 'could', are likely to be attributed to both learners' general tendency and L1 rhetoric, where certainty-oriented and collectivistic-oriented styles prevail.