The expression of time is fundamental in communication and languages have developed a variety of means to encode temporal relations. When learning a new language, learners are often faced with the challenging task of discovering a new system of temporal relations. The present study investigates the development of tense and aspect marking in the interlanguage of L3 Italian learners enrolled in university language courses. It examines how the tense-aspect system develops in the interlanguage and how the acquisition process is shaped by factors such as the lexical aspectual value of the predicates and discourse grounding. The data indicate that both lexical aspect and discourse grounding influence the distribution of verbal morphology in the interlanguage. Semantically congruent pairings of lexical aspect, verbal morphology and discourse grounding are used more frequently and appropriately than less prototypical combinations. The acquisition process is also influenced by the learner's L1, which was mostly German in the context of the present study. The study can be used as a guide for curricular decisions in language teaching, and for projecting further research on the development of tense-aspect marking in multilingual learners.