After a comprehensive description of the French and English tense, aspect, mood/modality (TAM) systems in Chapter 1, an overview of key theoretical perspective and applied perspectives from the morpheme-order studies to examples of internal and external interfaces in monolingual child acquisition is presented in Chapter 2. The literature review of L2 studies illustrates the subtleties of TAM properties in Chapter 3. It is followed by the rigorous methodology of a cross-sectional empirical study designed to test the L2 acquisition of the English TAM system along with pretest results in Chapter 4. The quantitative and qualitative analyses of data obtained from written production tasks, cloze tests and completion tasks completed by French EFL and ESL learners and a NS comparison group appear in Chapters 5, 6 and 7. The results discussed in Chapter 8 address the explanatory power of the Interface and Feature Reassembly hypotheses while directions for future research are offered in Chapter 9. Scholars will appreciate how new data carefully analyzed in its nuances and complexities bring us closer to better understanding the challenges L2 learners face.