Within the interdisciplinary mosaic of social and human sciences，issues of identityand second language usehave largely been researched as two independent fields. However，with growing mobility and migration around the world，the significance of exploring the interconnections between identity and second language use is becoming increasingly realized. Within this expanding area，researchers struggle to balance the fluid，highly abstract characteristics of identity with rigorous systematic academic approaches. Addressing this gap in research，this study utilizes a combination of reflective discourse analytic approaches and interactional discourse analytic approaches to investigate the relationship between identity and second language use in the context of Japan. This combination offers appropriately convincing detail in its data while still providing a richer and more compelling breadth of vision，therefore making the study holistic yet locally detailed in its focus.This book is composed of six chapters：an introductory overview component（Chapters recheck），a set of analytic findings on the data collected（Chapters 4—5），and a concluding discussion（Chapter 6）. In the first chapter，I clarify the motivations behind the study，which stem from the changes I noticed happening within myself as I used a second language. In order to explore the insights that other second language（L2）users held with regard to identity in second language use，there are two research questions promoted.（1）What can second language users’ narrative reflections tell us about the ways their identities change while using a second language？（2）How is the temporal co-construction of identity made visible through the details of second language interaction？After casting a critical eye on a sizable body of literature on second language use and identity，in Chapter 2 I situate the study within the qualitative tradition as a form of data-driven interpretative empirical research. I also outline the contributions and limitations of existing research in the field. Chapter 3 introduces the research design，prefacing it with a comparison of two broadly and inclusively defined methodologies：the reflective discourse analytic approach and the interactional discourse analytic approach. I then offer a profile of each of the seven participants：Carrie，Chin，Lee，Sam，Tasha，Wang and Yuan. The data collected in this research includes both the participants’ reflections and real-time second language interaction. The reflective data includes diary entries，interviews，email exchanges，transcripts of online chat sessions and journal entries. The interactional data is based on 30.5 hours of audio- and video-taped conversations between first language speakers of Japanese（L1）and second language speakers of Japanese（L2）. In the remaining two sections，I sketch out the data collection process and the analysis，discussing potential researcher biases and ethical considerations.Chapter 4 investigates how the participants perceive themselves while using a second language. Two main themes emerged in the data analysis：differenceand struggling . The findings demonstrate that the participants’ lives are affected by using a second language in the host country，indicating that one of the greatest significances of second language use in identity construction is that it offers a space in which participants can compare themselves to others. Feeling different is one of the bi-products of such comparison. The first part of the study focuses on how L2 users reported they have been assigned to a category named gaijin（foreigner）in a variety of contexts of Japan. This category is located in many different ways；it can become visible through subtle non-verbal like proxemics，or it can also be made evident through an individual’s choice of words. The aim here is not to judge whether the categorization is right or wrong，but on how the L2 users feel about their L2 interaction in various Japanese contexts.Chapter 5 provides a detailed sequential analysis which explicates the ways L1 speakers and L2 users can be seen to be “doing difference” and “doing sameness”，in mundane conversation with each other. In other words，addressing the second research question，the focus here is on ways that identity is made visible through talk. It was found that difference and sameness were made visible as interactional accomplishments via a closely interwoven network of linguistic and non-vocal conduct. These interactional cues affect the way subsequent sequences of talk unfurl，and therefore play a primary role in participants’ construction of self. I identified two types of “strategic sipping”which were astutely employed by interlocutors to manage both the turn-taking and the flow of consequent sequence of talk. By scrutinizing the sequential exchange of both verbal and embodied practices，I have demonstrated the ways difference and sameness are co-constructed in discourse by the interlocutors.Chapter 6 sums up the analysis and discusses directions for future research on second language use and identity，especially in the context of Japan. In the discussion，I argue that on the one hand，“L2 user”identity should not be a fixed label that is applicable to every situation and context and，on the other hand，it is only when we are sufficiently competent with the linguistic resources and become more conscious of our talk and the way it becomes a representation of ourselves，that we can begin to take more control of our circumstances and，eventually perhaps even become the ideal self we imagined we would become. Second language interaction offers a space for identity construction，in which diversity is not only unavoidable but also valuable. Although I have focused on L2 use，the accomplishment could be applied to other forms of vocal and non-vocal discourse. I conclude this chapter with some of the study’s implications for language education and future research.The findings of the study show us that individuals are not simply passive L2 users；they have their own philosophies，which lead them to critically engage with their experiences by observing and reflecting on the social contexts in which they find themselves.