Foreign language learning strategies are specific actions or techniques employed by the learner for the purpose of learning language, making learning easier, faster, more enjoyable, more self-directed, more effective, and more transferable to new situations, according to Rebecca Oxford. The paper presents a large scale project’s (THALES: 379335) first phase findings regarding the validation of Rebecca Oxford’s “Strategy Inventory for Language Learning”(SILL) with a Greek sample of1308 school-aged students from 16 schools representing 5 prefectures and 4 regions of the country. 46% of the students attended the last three grades of elementary school and 54% junior secondary school. Following a series of exploratory factor analyses we decided on a 29-item version retaining Oxford’s factor structure. The confirmatory factor analyses revealed a marginal level of fit for the whole sample as well as the elementary school and secondary school sub-samples. The analyses indicated moderate to high internal consistency coefficients for the two-and six-category model of the SILL instrument. Based on these findings a number of analyses were performed regarding differences across all the six SILL first-order categories (memory, cognitive compensation, metacognitive, affective, and social strategies) and the two second-order categories (direct and indirect strategies) in relation to gender and school level revealing significant differences. The results are discussed in relation to other similar studies and the next phases of the study.