Since grammar learning strategies (GLS) constitute a domain-specific manifestation of more broadly understood self-regulated strategic L2 learning (Pawlak, 2018b), it is only fitting to devote the first chapter of this book to an overview of research into language learning strategies (LLS) in general. Such research has evolved considerably over the last five decades and the numerous relevant studies have produced a vast wealth of invaluable empirical evidence (see Cohen, 2014; Cohen et al., 2023; Feng, 2025; Griffiths, 2018; Oxford, 2001, 2017; Oxford & Amerstorfer, 2018; Pawlak, 2021b; Pawlak & Oxford, 2018; Rose et al., 2018). For this reason, the overview provided in this chapter can only be brief and highly selective, focusing on issues and lines of inquiry that are the most germane to the main theme of this volume. Accordingly, at the very outset, the evolution of research into LLS will be outlined, highlighting the most crucial changes in how strategies have been conceptualized, the main research directions as well as methodological innovations. This will be followed by the discussion of the most influential classifications of LLS and the diverse way in which data on strategy use can be gathered in empirical studies. Subsequently, the focus will be shifted to a succinct overview of factors impacting strategy use that have been investigated by specialists and studies that have examined strategies in a domain-specific manner, with respect to learning specific target language (TL) subsystems and skills. The final section will be dedicated to strategy training or, to use the term preferred by many strategy experts, strategy-based instruction (SBI), synthesizing the findings of available studies and highlighting the decisions that have to be made when designing and implementing pedagogical interventions of this kind.