In this study we tracked the development of the "passe compose" in second-language learners of French whose first language is English. Although the "passe compose" is a highly used tense among native speakers of French and it appears to present particular difficulty for first-language English speakers, its second-language development has been surprisingly under-researched. In order to trace developmental patterns of the "passe compose" we obtained a corpus of obligatory context use of this tense by 30 Year-12 (lower-intermediate) students at two time points six months apart and analysed the data both quantitatively and qualitatively. Our findings suggest that these students used remarkably few memorized formulas, that they passed through five distinct stages in their acquisition of the "passe compose", that those early stages were characterized by transfer errors, and that the presence of the auxiliary, whether correct or incorrect, formed a crucial stage in the development of the tense. Theoretical explanations for the findings are presented together with some tentative pedagogical implications. (Contains 4 tables and 2 notes.)