This study investigates grammar learning strategies and the acquisition of L2 tense-aspect morphology through the retrospective think-aloud processes of a group of L3 learners of Catalan. A total of 18 students of Catalan in a university setting in Catalonia were asked to select one of three tense-aspect forms (preterite, imperfect, and perfect) in a short narrative written in the past. Retrospective think-aloud protocols were used to investigate what they were thinking when they made the decision to choose the appropriate tense-aspect form. A bottom-up analysis identified nine grammar learning strategies that participants used to select the appropriate past tense forms. The results on the frequency of use of the strategies show that they were often used in combination and that the most common ones were translation, aspect, adverbial, and tense strategies. The analysis of strategy use according to type of morphology and selection of the correct form in the narrative showed that strategy use is related both to specific tense-aspect forms as well as to accuracy in the selection of forms.