In the world today, expanding knowledge of sustainability is essential for promoting ESD and SL. To illuminate the evolution of ESD, the Stockholm Conference in 1972 was the first international conference that acknowledged the need for EE (UNESCO, 1972), indicating EE plays an important role addressing environmental issues (Lo et al., 2002; Sterling, 2013; Thomas et al., 1999). Followed by the Tbilisi Declaration that specified “EE should be provided for all ages at all levels” (UNESCO, 1978, p. 244), UNESCO (1978) mentioned that EE refers to “…knowledge, values, attitudes, and practical skills to participate in a responsible and effective way in anticipating and solving environmental problems” (p. 2). With this international endorsement, the term EE became increasingly widespread in the following decades. Arguably, during the 1970s and 1980s EE had a clear boundary on environmental issues, environmental interpretations, and environmental science (Sterling, 2013). To understand the change in terminology, accompanied by key milestones of ESD, Figure 1 illustrates a timeline with an overview of the evolution of ESD.

It is important to highlight the emerging interconnectedness between EE and other themes such as peace, justice, inequality, human rights, and development. As a result, the Brundtland Commission Report defined Sustainable Development as “development that meets the needs of the present without compromising the ability of future generations to meet their own needs” (Brundtland, 1987, p. 41), linking the concepts of “environment” and “development” in the contextualization of EE and ESD respectively. Consequently, as the Rio Summit stated, “the need to re-orient Education for Sustainable Development (ESD)” (United Nations, 1992), during the 1990s a broader perspective of EE arose. Subsequently, on December 20th, 2002, the United Nations General Assembly declared 2005–2014 as the Decade of Education for Sustainable Development (DESD) (UNESCO, 2004; ESD Section, 2007).

In three decades, from 1972 to 2002, the concept of EE evolved into ESD. Currently, the UNESCO Office Venice, and Regional Bureau for Science and Culture in Europe (2024) states that ESD “gives learners of all ages the knowledge, skills, values and agency to address interconnected global challenges including climate change, loss of biodiversity, unsustainable use of resources, and inequality” (p. 11). Since ESD encompasses environmental, social and economic dimensions, the use of the term ESD has gained increasing influence worldwide, particularly after the United Nations launched Agenda 2030 including 17 SDGs (United Nations, 2022).

Although EE, Education for Sustainability, and ESD are utilized in the literature as interchangeable terms (Adlong, 2013; Rukmana et al., 2023; Sterling, 2013), it is relevant to mention that consensus on the terminology of EE, Sustainability Education, Sustainable Education, and Education for Sustainability has not yet been reached. For instance, while Barkemeyer et al. (2014) noted that sustainable development discourse tends to emphasize environmental over social aspects, Kopnina (2014) argued focusing on social aspects often overlooks the environmental perspective.

In addition, Sterling (2013) highlighted various perspectives in the ongoing debate regarding the terms EE or ESD: some argue EE is synonymous with ESD, others contend ESD is a component of EE or vice versa, and some suggest ESD is a holistic term while EE should be discarded. For example, whereas De Andrade Guerra et al. (2018) found commonalities between the two terms EE and ESD and treated them as synonymous, Ilovan et al. (2019) utilized the terms of EE and ESD with defined characteristics, and Holm et al. (2015) employed only the term ESD, leaving out term EE. Despite these differing viewpoints, the transition from EE to ESD remains an evolving topic.

Acosta Castellanos and Queiruga-Dios (2022) confirmed two predominant currents in the literature: EE and ESD, noting that Europe is the most noticeable geographical region transitioning from EE to ESD. However, this result does not imply that EE is outdated, as the other regions in the world (Asia, North America, Oceania, Africa, and Latin America) still produce publications using this term (Acosta Castellanos and Queiruga-Dios, 2022). Consequently, it is expected that scholars continue to generate research on ESD, which is the most prominent stream (Acosta Castellanos and Queiruga-Dios, 2022), as part of the agenda 2030 that includes the global efforts to work on the sustainable development of goals.

As UNESCO (2017) stated, ESD should be integrated into all curricula in formal education across all levels. Even though the labels are important to achieve coherence and a shared understanding of the meaning of ESD, there is an urgent need to develop training and expand sustainability knowledge that translates to pro-sustainable behavioral change (Kuehl et al., 2021; Chen C. et al., 2022; Décamps et al., 2017; Sanchez et al., 2024) as well as embrace SL at all education levels (Potter-Nelson and Meyers, 2022; Leiva-Brondo et al., 2022; Sanchez et al., 2024).

The conceptual dialogue surrounding SL is intrinsically linked to the United Nations' SDGs and the framework of ESD, all of which are crucial in accomplishing sustainable development and achieving the SDGs (Ahel and Schirmer, 2023). Systematically, SL is an outcome of ESD (Décamps et al., 2021), and EL is an outcome of EE (Elder, 2003; Moody et al., 2005). Since the literature about the definition of SL is fragmented, this research contributes to a better understanding of the notion of SL and EL in the context of ESD. To clarify the concepts and learning outcomes of SL and EL, this study will develop a SLR that serves as a robust and comprehensive methodology for critically appraising research, positioning it on par with high-caliber primary studies (Petticrew, 2001).

Previous studies have focused on EL and the eco social crisis (Martínez-Aznar et al., 2022) as well as studies probing the modeling of EL among university students (Aighewi and Osaigbovo, 2010; Teksoz et al., 2012). Therefore, this literature review embarks on a pioneering effort to explore the notions of SL and EL, highlighting the most cited definitions, associated concepts, and the most representative networks and author collaborations.

Adhering to the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) (Page et al., 2021; Liberati et al., 2009), the search strategy was conducted between August 2023 and September 2023. The search for articles was conducted in two specific databases, Scopus and Web of Science. Google Scholar database was not utilized to search for the articles. This SLR employs high-quality journals. Fleming et al. (2014) mentioned that these journals generally offer higher methodological quality. In addition, high-quality journals typically undergo rigorous peer-review process (Abushouk et al., 2021), which enhance validity, reliability, and relevant of the research they publish. Moreover, these journals often require informing adherence to reporting standards and checklists such as EQUATOR, PRISMA, or MOOSE to ensure transparency and rigor (Abushouk et al., 2021). Furthermore, high-quality journals are more likely to publish research that meets rigorous scientific and methodological standards, providing robust statistical analyses and meaningful contributions to the field.

The search strategies were highly targeted and precisely designed to examine SL and EL definitions in scholarship conducted or associated with higher education institutions. Therefore, the search equation comprised (“Universit^*” OR “higher education institution” OR “institution of higher learning”) AND (“sustainability literacy” OR “sustainability-literate” OR “sustainability literate” OR “sustainability proficiency” OR “environmental literacy” OR “sustainability litera^*” OR “sustainability literacy assessment” OR “sustainability literacy measurement” OR “environmental litera^*”). These search terms resulted in 441 articles from the selected databases (Scopus and Web of Science).

Figure 2 summarizes the stages of the article's selection process. Initial results reported 441 articles from both databases, encompassing quantitative, qualitative, and mixed methodologies studies published between 1982 and 2022.

The authors reviewed all 441 articles of the initial search and removed 184 duplicates, leaving 257 articles. Subsequently, we screened the abstracts of these 257 articles to ensure their relevance to the objectives of the systematic review. After carefully reading the abstracts, we excluded 156 articles that were not relevant to the research focus, resulting in a final set of 101 articles that aligned with the purpose of the study. The abstract screening helped us initially filter articles for relevance before proceeding to a full-text review. Articles were excluded based on irrelevant topics or focus, poor reporting, or methodological flaws.

Initial inclusion criteria were set for articles published in journals and papers in their final stage that offered full text and were subjected to peer-review and available in either English or Spanish. Essential details like title, abstract, keywords, authors' credentials, journal designation, and publication year of the discerned records were cataloged in a Microsoft Excel spreadsheet. Next, the authors read 101 articles searching for definitions of SL and EL. As a result, 27 publications were excluded because they did not provide definitions of either SL or EL.

Subsequently, 74 articles underwent evaluations, categorizing them based on relevance to the topic. To ensure sources were of the highest quality and rigorously researched and reviewed, the next set of selected papers were those that had been published in journals ranking in the Journal Citation Report (JCR) or Scimago Journal Ranking (SJR) quartile 1 (Q1) and quartile 2 (Q2). This classification helps to understand credibility, impact, and standardized evaluation of the articles selected. A meticulous investigation of the remaining articles was conducted to further validate their pertinence, culminating in a final list of 38 articles. This research aimed to examine peer-reviewed journal articles as opposed to other sources that may contain SL and EL information, such as university and departmental mission statements or instructor syllabi because these items are more difficult and elusive to obtain, are unstandardized, and can be changed and updated frequently. Relying on high-quality, well-researched published materials is a more reliable way to incorporate previous researchers' findings. The eligible sample is composed of 38 articles published in high quality journals ranked in Q1 and Q2 by the JCR and the SJR.

This study adopted PRISMA guidelines set forth by Page et al. (2021) to develop a structured literature review which employed a qualitative thematic analysis approach (Miles and Huberman, 1994) to analyze the data. Data was coded using the software ATLAS.ti version 23. The process to analyze the definitions of SL and EL is as follows:

The authors used deductive coding, in which themes were identified and reviewed. The principal investigator read the full-texts articles, developed the coding system, communicated the coding strategy to the co-authors, trained the co-authors to perform the thematic analysis, and assigned a data set to each member. To ensure reliability, the data were coded independently by two co-authors. Each coder saved the coding in an independent bundle file, which afterwards was merged into the master file. To reduce any bias in the analysis, the Intercoder Agreement (ICA) percentage was calculated using ATLAS.ti version 23. As a result, the Krippendorff's c-Alpha-binary was 0.94.

The concept of EL proposed by Roth (1992) is the most cited definition which states, “the capacity to perceive and interpret the relative health of environmental systems and take appropriate action to maintain, restore, or improve the health of those systems” (p. 10). Table 1 shows the most cited definitions of SL and EL in the literature subject to this study. Even though SL and EL are related concepts, the concept of EL precedes SL. In addition, the definition of SL is more consistent with the broader concept of sustainability. In this sense, the foundational concept and framework of SL encompasses vital insights into social, environmental, and economic sustainability, which increases the complexity of the concept. As a result, Nolet (2009) mentioned, “Sustainability literacy is construed generally here as the ability and disposition to engage in thinking, problem solving, decision making, and actions associated with achieving sustainability” (p. 421).

The typology of definitions of SL and EL based on specific learning outcomes provides a framework to understanding the similarities and features supported in the literature. Thus, this research illuminates the prevailing discourse of the notion of SL, highlighting its definitions and specific learning outcomes to the ESD. As it is exhibited in Table 2, the foundational concept of both SL and EL includes knowledge, awareness, attitudes, skills, and behaviors toward sustainability, being the environmental dimension the intersection between EE and ESD.

In addition, Appendix A shows the description of the 38 studies analyzed, the classification of those articles according to the definition of either SL or EL, and the methodology used in each paper. The 38 articles contain 25 articles focused on EL and 13 articles focused on SL. The most predominant research design in the sample of articles is quantitative research design. Six articles used mixed methods (MM) research design, four employed qualitative design (QUAL), and 20 used quantitative design (QUAN). Most of the studies were published in journals that focused on sustainability and education; environmental, cultural, economic, social sustainability; and policy and practice research. The audiences are mainly researchers, scholars, academics, students, teachers, and policy makers.

The discourse on SL and EL in non-English speaking countries is influenced by both global and specific contexts, as well as unique educational settings. This SLR included research applied in countries where English was not the primary language, such as China, Taiwan, Brazil, France, Nigeria, and the Czech Republic. A commonality among all those studies is the alignment to the global concern of expanding sustainability and environmental knowledge.

The research applied in non-English speaking contexts is associated with the ongoing international debate of using the terms SL or EL. In countries such as Brazil, Nigeria, France, and Czech Republic, the common term used was SL. In contrast, China and Taiwan used the term EL. On the one hand, Fang et al. (2018) highlighted the need to train environmentally conscious citizens with high-quality EL in Taiwan. On the other hand, Caldana et al. (2023) mentioned the importance of establishing more formal rules and educational policy to integrate SL throughout the business management, economics, and accounting curricula in Brazil. In addition, Akeel et al. (2019) pointed out the need to improve SL in Nigeria, and Tunji-Olayeni et al. (2023) noted the dearth of studies focused on SL in Nigeria. Décamps et al. (2021) cited the need to measure sustainability knowledge worldwide. The research identifies how non-English speaking countries are working on SL and EL to address local and global problems as well as to contribute to the SDGs.

The co-occurrence of the authors' keywords was applied to the sample of the 38 articles. To gain a better understanding of the associated concepts to SL and EL, the authors conducted a co-occurrence network analysis. Data was analyzed using the R Studio software version 4.3.0, biblioshiny, and bibliometrix, which are open-source computer software (Aria and Cuccurullo, 2017). Figure 3 shows two clusters of the co-occurrence network. Cluster 1, shown in red, is composed of three major words: higher education, sustainability literacy, and sustainable development goals. Knowledge is one of the major outcomes of SL. Increasing SL in higher education institutions implies expanding students' sustainability knowledge which is directly related to enhancing students' knowledge of sustainability development goals. There is a strong relationship among SL, sustainable development goals, and higher education.

On the other hand, Cluster 2, shown in blue, exhibits the interconnection among the following terms: EL, EE, sustainability, education for sustainability, and curriculum. EL is a learning outcome of EE; likewise, SL is a learning outcome of Education for Sustainability or ESD. The central node, EL, is consistent with literature in the sample because 21 out of 38 articles were directly related to the concept of EL.

In this study, the collaboration network by countries refers to how authors from different countries collaboratively work on a research topic based on co-authorship patterns. These collaborations allow the creation of connections through joint publications on an international scale and identify which countries have the greatest connections and which countries are leading research on a specific topic.

Exploring the social structures of the field, collaboration among scholars across countries is an important factor in strengthening research networks. Understanding how scholars interact among themselves helps to map potential clusters and institutional partnerships to enhance research (Donthu et al., 2021). Figure 4 illuminates these collaboration networks by countries. The United States shows a greater effort in strengthening collaborative research bonds with countries such as Turkey, Canada, and Nigeria. Nigeria extends connections with South Africa, while the United Kingdom and France are working together on sustainability research projects. Finally, researchers in China tend to collaborate with scholars from Australia and Thailand.