This study examines the distribution and functions of the polysemous adverb just in academic written English, focusing on disciplinary variation and the interaction with the writer’s English competence. A corpus consisting of research articles published in both overseas and domestic journals was compiled from three disciplines: English literature, applied linguistics, and science and engineering. The meaning categories of just were classified into six groups: exclusive focus markers, particularizers (specificatory, comparative, exact), diminishers, and emphasizers. The analysis of the corpus showed that the frequency of just was very low compared to spoken academic English. Among the three disciplines, literature articles contained the highest tokens of just, converging to the observation that the writing style of this field is rather informal. Each discipline had its own preference regarding the meaning categories and collocational patterns, reflecting the characteristics of the discipline. Non-native writers differed from their native counterparts in their use of just in accordance with discipline-specific patterns. Overall, the use of just is shown to be influenced by various factors, such as text type, discipline-specific writing style, and the writer’s English competence. Future research comparing the functions of just and similar adverbs (e.g. only, merely) is expected to provide a more comprehensive picture of the behavior of this small word.