1. Introduction

Second language acquisition (SLA) research has historically prioritized classroom-based contexts, with the exception of areas such as study abroad, incidental and self-directed learning. In the last decades, however, research interest in second language (L2) learning beyond the classroom has grown substantially, expanding our understanding of where and how L2 learning takes place. This can be largely attributed to advancements in mobile and digital technologies which, through rapidly expanding access to online content, have opened up new possibilities for authentic L2 consumption, production, and interaction. Researchers coined various terms to describe these new avenues of online language use, including online informal learning of English (OILE; Toffoli & Sockett, 2010*Footnote ¹), informal digital learning of English (IDLE; Lee & Dressman, 2018*), out-of-class language learning with technology (Lai & Gu, 2011*), or language learning in the digital wilds (Sauro & Zourou, Reference Sauro and Zourou2019). In parallel, other researchers began to investigate extramural English (EE; Sundqvist, 2009*) and language learning and teaching beyond the classroom (LLTBC or simply LBC; Reinders & Benson, 2017*; Reinders et al., Reference Reinders, Lai and Sundqvist2022a), with similar overall research objectives but a broader focus that includes both digital and “real-world” practices. Since then, the number of publications on language learning beyond the classroom has increased exponentially, with particularly rapid growth since 2017 (Kusyk et al., 2025*). From this body of literature, the beginning contours of what we will refer to as informal second language learning (ISLL; Arndt, Reference Arndt2019) as a distinctive area of interest within SLA research have emerged. Different varieties of learning outside the classroom both overlap and differ considerably in their definitions. They can be distinguished by four primary aspects (see Fig. 1), referring to the inclusion of non-formal activities in addition to informal activities; activities that are teacher-initiated or link to the formal language classroom in addition to learner-initiated and -direct activities; “real-world” activities in addition to digital or technology-mediated activities; and other target languages in addition to English. Figure 1 presents an overview of how the most frequently cited terms differ in regard to these aspects, based on our interpretation of the definitions provided in the literature. LLTBC being the most inclusive term (Reinders et al., Reference Reinders, Lai and Sundqvist2022a), we consider it an umbrella under which the other terms can be subsumed.

*Some later publications included activities not mediated by technology (e.g., Lai, Reference Lai2015). ºWhile Lee (Reference Lee2019b) distinguished between IDLE in extracurricular vs. extramural contexts, the former retaining a link to formal and non-formal language education, a later publication defines IDLE as “a fully autonomous L2 activity in out-of-class digital environments that is not linked to formal language instruction” (Lee, 2020*, p. 52).

Figure 1. Language learning and teaching beyond the classroom: Terms and definitions.

In this timeline we focus on the particular strand of ISLL, which we define as follows:

• • Informal refers to autonomous, self-initiated participation in L2 activities beyond the classroom, both on- and offline, which are unconnected to language courses or other forms of formalized learning and teaching (e.g., private tutoring). In this sense, we exclude non-formal learning (programs and resources designed for learning outside of educational institutions, e.g., online language learning communities or language learning apps; Schugurensky, Reference Schugurensky2007) because it may involve different learning processes and levels of motivation than informal learning.

• • Second language is used symbolically, as in second language acquisition, to refer to all additional languages (L2, L3, etc., or L_n) learned both in traditional second language and foreign language contexts. The term also indicates a consideration of many possible target languages, as opposed to focusing just on English.

• • Finally, learning here refers to language development in all forms (acquisition, learning, progression, regression, etc.), also taking into consideration psychological variables connected to the learning process such as motivation, grit, willingness to communicate, etc. Learning may take place intentionally, though it is often incidental, emerging from participation in meaning-focused activities.

The timeline is intended to help readers familiarize themselves with the topic of ISLL, as defined above, through presenting a selection of research papers, theoretical discussions, reviews, etc. that includes influential, widely cited works that have shaped this research area, articles representing a cross-section of the topics that the field has grappled with in this time, and those that signify important milestones or conceptual developments in ISLL research. We also include some publications that underscore the evolution of pedagogical practices as a result of the growing importance of ISLL (e.g., Lai, 2019*; Richards, 2015*; Thorne & Hellerman, 2022*). Though concerned with the classroom, rather than informal settings, these publications emphasize the importance of learner autonomy, learner choice, and bidirectional learning across the formal–informal interface.

To be sure, SLA researchers have been interested in language learning beyond the classroom long before the recent surge of ISLL-related publications: consider Bialystok (Reference Bialystok1981) underlining the importance of functional practice through language exposure in promoting L2 competence; discussions on autonomy and the importance of learning beyond the classroom (Benson, Reference Benson2001; Hyland, Reference Hyland2004); and studies on face-to-face interactions (Brouwer, Reference Brouwer2003; Spada, Reference Spada1986) and language learners’ use of traditional media (Murphy, Reference Murphy2005; Pickard, Reference Pickard1996). Learning through leisure has also been investigated extensively in the context of television viewing, especially in Europe where countries employ different broadcasting modalities such as subtitling, captions, and dubbing (e.g., European Commission, 2011; Koolstra & Beentjes, Reference Koolstra and Beentjes1999; Vanderplank, Reference Vanderplank1988). In the early 2000s, the field of new literacies explored questions of digital L2 literacy and identity construction through participation in chat rooms and online communities (e.g., Black, Reference Black2006; Lam, Reference Lam2000). Around the same time, broader investigations of out-of-class L2 exposure and use with various technologies began to emerge, which we take as the point of departure for this timeline (e.g., Alabau et al., 2002*; Lamb, Reference Lamb2004). While echoing themes and insights from earlier scholarship, these more recent studies generally aim to investigate informal language learning in a more holistic manner, transcending individual technologies to paint a comprehensive picture of learners’ language exposure and use outside the classroom and, in some cases, relate it to different aspects of language development and individual learner differences.

In addition to recognizing that ISLL research is rooted in studies dating back far beyond the beginning of this timeline, it is also important to distinguish between the foci of ISLL research and certain “ISLL-adjacent” areas of inquiry. Firstly, we have observed a considerable amount of overlap with computer- and mobile-assisted language learning (CALL/MALL), with some ISLL studies even situating themselves within the greater CALL/MALL landscape (e.g., Benson & Chik, Reference Benson and Chik2011; Lee, Reference Lee2019a). This overlap could sow some confusion, with the strong tendency of CALL/MALL studies to focus on the use of mobile learning applications in the classroom, or in teacher-led non-formal contexts, as well as on the devices themselves (Burston, Reference Burston2014; Chwo et al., Reference Chwo, Marek and Wu2016). Though there is certainly utility in examining ISLL as a possible complement to classroom pedagogy (see, e.g., Lee & Sylvén, 2021*; Richards, 2015*; Thorne & Hellermann, 2022* on the interface between informal and formal learning), in keeping with our definition of ISLL above, we have excluded publications from our timeline which would be better situated within CALL/MALL because they focus primarily on digital practices connected to classroom or teacher-led activities. We also exclude studies on L2 learning in study abroad and migration. While the potential for learning through informal language exposure and use certainly exists in these contexts, we feel that they are firmly rooted within SLA as distinct areas of inquiry with their own historical development and bodies of literature. Finally, while the timeline is limited to journal articles and book chapters, interested readers should not overlook relevant monographs and edited volumes, such as Benson and Reinders (Reference Benson and Reinders2011), Nunan and Richards (Reference Nunan and Richards2015), Sockett (Reference Sockett2014), Sundqvist and Sylvén (Reference Sundqvist and Sylvén2016), Dressman and Sadler (Reference Dressman and Sadler2020), plus additional collections mentioned in the timeline.

Despite being a relatively new area of inquiry within SLA, a clear evolution in research interests, objectives, and methodologies can be observed in recent ISLL studies. We have previously proposed that these changes can be grouped into three major waves (Kusyk et al., 2025*), which is clearly reflected in the timeline: Research published in the early 2010s primarily centered on the discovery and description of ISLL, using questionnaires to inventory learners’ informal habits, their frequency, and perceptions of informal L2 use (e.g., Lai & Gu, 2011*; Sundqvist, 2009*, Toffoli & Sockett, 2010*). In the second wave, the focus shifted toward the relationships between informal L2 practices and language learning, with findings overwhelmingly pointing toward positive associations (e.g., Cole & Vanderplank, 2016*; De Wilde et al., 2020*; Peters, 2018*). This is often interpreted as evidence that informal L2 exposure and use benefit language learning, although the heavy reliance on correlational methods means that the proposed causal relationship requires further investigation (e.g., in longitudinal studies, see Bengtsson, 2023*; Kusyk, Reference Kusyk2017). Research in the most recent third wave shifted toward exploring ISLL in relation to numerous individual difference (ID) variables and the nature of specific informal activities themselves, in order to determine for whom and under which conditions ISLL can be most effective (e.g., Arndt, Reference Arndt, Toffoli, Sockett and Kusyk2023; Lai, Reference Lai2015; Lee & Hsieh, 2019*). Since the “first wave,” studies have also increasingly incorporated more complex methods and forms of analysis, such as multilevel linear regression, structural equation modelling, and latent profile analysis (e.g., Arndt, Reference Arndt2019; Lee, 2020*; Liu & Ma, 2024*).

We see the evolution of research themes and methods, including a push for standardized instruments developed specifically for research in informal contexts (Arndt, 2023*; Sockett et al., Reference Sockett, Yibokou and Schofield2023; Sundqvist & Uztosun, 2024*), as a sign that ISLL research as a whole is growing and maturing. The publication of several systematic and scoping reviews (e.g., Kusyk et al., 2025*; Zhang et al., 2021*) and comparative studies (e.g., Muñoz & Cadierno, 2021*; Sundqvist & Uztosun, 2024*) would lend support to this suggestion. Finally, recent papers on new technologies (e.g., generative artificial intelligence: Liu & Ma, 2024*) and languages other than English (e.g., Japanese: Bengtsson, 2023*) illustrate the direction in which the literature is currently developing.

In summary, this timeline is intended to chronicle the recent historical development of research within informal second language learning, highlighting key contributions and significant findings along the way. We categorize the publications according to the following themes that emerged through our systematic readings and observations of the literature:

A. Publication focus

1. 1. Research review

2. 2. The formal–informal interface

3. 3. Theorizing ISLL

4. 4. Research methods

B. Research focus

1. 1. Describing/inventorying informal practices

2. 2. Learner/teacher perceptions

3. 3. Correlations between informal practices and proficiency/ID variables

4. 4. Group comparisons

5. 5. Case studies

6. 6. Learners prior to instruction

7. 7. Longitudinal investigations

C. Aspects of informal practices

1. 1. Frequency (how often)

2. 2. Duration (time spent)

3. 3. Diversity

4. 4. Quality (nature of engagement with these resources)

D. Aspects of language proficiency

1. 1. General proficiency

2. 2. Vocabulary

3. 3. Grammar

4. 4. Reading

5. 5. Writing

6. 6. Listening

7. 7. Speaking

E. Individual differences

1. 1. Gender

2. 2. Self-efficacy, confidence, grit

3. 3. Emotions: Anxiety, enjoyment

4. 4. Motivation, attitudes, willingness to communicate