Chapter 1 discusses first and second language acquisition, and language acquisition by adult and child learners.
This book introduces how second language acquisition research is being conducted based on various research methods and theoretical backgrounds in fields such as linguistics, psycholinguistics, and sociolinguistics, and organizes the content by presenting terminology, etc.
In Chapter 2, we analyzed related research focusing on the field of linguistics to find an answer to the question of what systematically determines the linguistic constraints that occur in the process of forming second language grammar.
In the field of linguistics, hypotheses and theories on second language acquisition were introduced based on theories such as contrastive analysis, error analysis, interlanguage, universal grammar and markedness, and functional typology.

Chapter 3 introduces how second language acquisition research is being conducted in the field of psycholinguistics.
In relation to cognitive domain and neurolinguistics research, the hemispheric polarization of the brain, critical periods, etc. were introduced, and further theories on the language learning process, language acquisition sequence, input and output processes, etc. were introduced.
We also describe and provide various examples of studies related to learning motivation, learning styles, and learning strategies that focus on learner variables rather than teacher variables.
Chapter 4 introduces how research on second language acquisition is being conducted in the field of sociolinguistics.
Chapter 5 summarizes the second language acquisition theories discussed previously.
We also discussed various research methods, including qualitative research, quantitative research, and observational research, in data analysis for second language acquisition research.

Chapter 1 provides a general introduction to how the theoretical foundations of research on second language acquisition have been developed organically and integratively in the fields of linguistics, psychology, and sociology.
The differences and similarities between first and second language acquisition are explained, and the language acquisition process of child and adult learners is described.
In addition, we introduced and presented directions for the development of educational materials for Korean language acquisition, cognitive ability, language and identity, and language education for overseas Korean children.
--- From "Enter"

Second Language AcquisitionThe fundamental questions researchers have in understanding the second language acquisition process are: What is second language acquisition? What process do second language learners go through to learn a language? How do second and first language acquisition differ?
Second language acquisition research began as an independent discipline in the 1970s, but has made remarkable progress in the short period since.

Second language acquisition research studies how and through what process a second language is learned.
It is a study of how learners learn a new language system in an artificial environment, what is learned and what is not, and why it is not acquired like a native language.
Second language acquisition research is an interdisciplinary field in which theories from various fields, including linguistics, psychology, sociology, sociolinguistics, and education, influence each other.

Second language acquisition research, in the field of linguistics, has examined linguistic constraints on second language pronunciation, vocabulary, and grammar formation.
In the field of language education, the results of language acquisition research are influencing curriculum design.
Cognitive Psychology In the field of cognitive psychology, discussions are taking place on language input and output, learners' affective factors, and the order of language acquisition.
In the field of sociolinguistics, research is being conducted on discourse, pragmatics, and linguistic etiquette between native and non-native speakers in terms of intercultural communication, and research is also being conducted on bilingual/multilingual language acquisition in relation to language policy.
Second language acquisition research is a complex field that involves abstract linguistic theories.
In each field, data on second language acquisition are collected and analyzed in various ways, and the research results are interpreted in various ways using different approaches.
--- 「1.1.
From “Research on Second Language Acquisition”

A major goal of second language acquisition research is to systematically explain the linguistic constraints that occur during the formation of second language grammar.
In the field of linguistics, the study of human language knowledge, including language creation and the limitations of language variation, is not limited to the first language but also includes the second language.
In the field of linguistics, research on second language acquisition has been conducted based on theories such as contrastive analysis, error analysis, interlanguage, universal grammar and markedness, and functional typology.
--- From "Linguistics"

In the field of psycholinguistics, the study of cognitive domains, neurolinguistics, and hemispheric lateralization of the brain, critical periods, etc. were discussed, and later theories were formed by analyzing data in the fields of language learning process, language acquisition sequence, input and output, etc.
As the focus shifts to learner variables rather than teacher variables, research is being conducted on learning motivation, learning styles, and learning strategies.
--- From "Psycholinguistics"

SociolinguisticsThe field of sociolinguistics examines the influence of social variables on interlanguage development.
Research is being conducted on sociolinguistic transfer phenomena that occur in the process of second language acquisition, communication skills, language input and interaction, sociocultural theory, bilingualism and identity, and how the institutional power and constraints of a country affect language use.
--- From "Sociolinguistics"

Language education is a field that requires methodological knowledge about language learning.
It is a field that studies how language learning occurs through language teaching methods.
Second language acquisition research has contributed to the recognition in language curriculum design that language learning involves more than just memorizing grammar rules.
It contributed to a new and broad concept of the nature of language learning.
For example, if a teacher has students learn a specific grammar structure by repeatedly practicing it during class, but then, after class, when speaking with the teacher, the students produce a different grammar structure from what they just learned, the cause of this can be examined from various angles.

--- From "Language Education"