This edited volume offers a systematic and critical examination of how theories in second language acquisition have been formulated, justified, and sustained, with particular attention to their status as explanatory accounts. Rather than introducing theories in isolation, the chapters revisit influential hypotheses and frameworks across linguistic, psycholinguistic, and cognitive approaches, asking what they genuinely explain, what assumptions they rely on, and where their limits lie. The book brings together multiple interdisciplinary perspectives, unified by a shared concern with theory construction and evaluation. Its aim is not to propose a single new model, but to sharpen conceptual foundations and to clarify productive directions for future research. Intended for graduate students and early- to mid-career researchers in SLA and related fields, the volume complements existing handbooks by providing a rigorously critical update to debates that have remained largely unchanged since earlier landmark works such as Long’s Problems in SLA.

This edited volume offers a systematic and critical examination of how theories in second language acquisition have been formulated, justified, and sustained, with particular attention to their status as explanatory accounts. Rather than introducing theories in isolation, the chapters revisit influential hypotheses and frameworks across linguistic, psycholinguistic, and cognitive approaches, asking what they genuinely explain, what assumptions they rely on, and where their limits lie. The book brings together multiple interdisciplinary perspectives, unified by a shared concern with theory construction and evaluation. Its aim is not to propose a single new model, but to sharpen conceptual foundations and to clarify productive directions for future research. Intended for graduate students and early- to mid-career researchers in SLA and related fields, the volume complements existing handbooks by providing a rigorously critical update to debates that have remained largely unchanged since earlier landmark works such as Long’s Problems in SLA.