Abstract
<jats:title>Abstract</jats:title> <jats:p>Usage‐based accounts of second language acquisition (SLA) are widely understood to conceptualize language learning as the construction of form‐meaning mappings through exposure and meaningful interaction, supported by domain‐general cognitive mechanisms. This entry outlines the core assumptions and learning mechanisms central to usage‐based SLA theory. Language forms are understood as constructions—ranging from simple words to complex syntactic patterns—that are socially learned and conventional within speaker communities. Importantly, second language development requires both exposure to the target language and opportunities for situated language use. Some key socio‐cognitive learning mechanisms are examined: frequency‐sensitive learning, categorization, learned attention, and blocking. These mechanisms interact to shape L2 developmental trajectories, with prior linguistic knowledge critically influencing the routes and rates of new language learning. Nevertheless, the entry emphasizes that no single mechanism adequately explains L2 outcomes.</jats:p>