Ability to infer the meaning of unknown words encountered while reading plays an important role in learners' L2 word-knowledge development. Despite numerous findings reported on word-meaning inference, how learners develop this ability is still unclear. In order to provide a developmental inquiry into L2 word-meaning inference while reading, this study examined 5 Japanese college-level ESL learners' meaning-inference behaviors for a 4 week period, focusing on their inference success rates and strategy use. The learners were engaged in a weekly reading and meaning-inference session, in which they read an academic text for comprehension, identified unknown words in the text, and inferred the meanings of the unknown words. The think-aloud technique was used to observe their meaning-inference performance. The results demonstrated that (a) the learner who had the lowest score on a reading comprehension test showed a constant increase in success rate, the number of strategies used, and the variety of strategy types used; (b) the more successful learners did not show a considerable change but had a more structured approach; and (c) the learners showed a shift from local strategies to global strategies. Pedagogical implications of these findings are discussed in terms of training effect. (Contains 10 figures and 4 tables.)