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This paper focuses on cross-linguistic influence (= CLI) in Second Language Acquisition (= SLA). More specifically, it aims at promoting a deeper understanding of the many dimensions of this phenomenon by (second language) teachers of multilingual classrooms. First, CLI is defined and presented in its multifaceted aspects. Positive and negative outcomes of CLI, its overt and covert instances occurrence and its psychotypology are outlined by means of examples in Italian as an L2. Positive and negative outcomes of CLI are described, with overt and covert instances and its psychotypology being outlined by means of examples in Italian as an L2. The negative consequences of either the failure to recognize instances of CLI or the incorrect classification of learners’ errors as instances of CLI are illustrated in the second section. Finally, some resources are suggested for second language teachers to improve their understanding of CLI in the output of learners of Italian as an L2."