In this contribution, we provide a critical reassessment of multilingual advantages, especially in the context of learning additional languages. Although there is widespread agreement that multilingual experience enhances language learning, a precise definition of the relevant conditions remains a challenge. After a topical overview, we discuss several case studies focusing on language learning advantages, interdependence, and cross-linguistic influence in different multilingual constellations. This discussion covers contexts of balanced bilingualism, heritage bilingualism, institutionally planned multilingualism, minority language bilingualism, as well as multilingual settings in which English is used as a Lingua Franca. In addition, we elaborate on two conditions (type of bilingualism, type of language knowledge) that impact language learning in multilingual settings. It is important to distinguish between balanced and unbalanced bilinguals as well as general language proficiencies and grammatical knowledge. On the whole, this paper is a warning against foregone conclusions and an invitation to a more thoughtful approach to a highly fascinating field.