Lots of studies have tried to test the effect of strategy training on vocabulary development. However, instead of trying to uncover the strategies that learners actually use, they have tried to expose learners to a list of strategies supported by theories. Although these theory-driven studies have provided the field with significant and generalizable findings, they have deprived it from a deep understanding of vocabulary learning strategies. To fill in this gap, this data-driven study aims at conceptualizing learners' vocabulary learning strategies. To uncover learners' knowledge and use of these strategies, the researchers iteratively collected and analyzed data through open-ended interviews. The rigorous coding schemes of grounded theory yielded a set of categories conceptualizing learners' awareness and use of vocabulary learning strategies. Although inspiring, the findings show that learners use a limited number of strategies and this clearly explains lexical deficiency among a great number of Iranian EFL learners. This conceptualization of strategy use has clear implications for policy-makers, practitioners and language learners.