|Abstract:||Morphological gemination consists of the systematic gemination of a segment associated with the systematic change in meaning of the affected base? (Samek-Lodovici, 1993). In Moroccan Arabic, morphological gemination characterizes the derivation of causative verbs, agent nouns and instrument nouns. It involves the lengthening of the second segment of some base root to express the intended morphological function. (e.g. ktb 'to write' >> kəttəb 'to make write'). In the case of the agent and the instrument, lengthening the second segment is espoused with the presence of some vocalic material, namely the vowel /a/ (e.g. fəllaħ 'farmer' and səmmaʕa 'headset'). Using the constraint-based framework of Optimality Theory, this paper will try to answer the following questions: (i) What is the morphological process responsible for morphological gemination in Moroccan Arabic? (ii) What is the morphological exponence of the causative, agent and instrument morphemes? (iii) How does the templatic shape of each form come to be?