Among many topics in sociolinguistics, many discourse studies have been carried out to explore how social factors are related to the use of language. The purpose of this research is examine assumptions, methods, and major topics/issues of the following discourse approaches to sociolinguistics: (i) interactional sociolinguistics, (ii) ethnography of speaking/communication, (iii) variation analysis, (iv) conversation analysis, and (v) critical discourse analysis, among others. In doing so, this paper first examines the developmental history of sociolinguistic research in discourse, discussing researchers' interest in discourse in exploring social activities and practices. After that, it starts with the interactional sociolinguistic approach to discourse analysis, discussing the notion such as Gumperz's contextualization cues. It also discusses Hymes' theory of ethnograpy of speaking/communication in exploring the relationship between communication and social contexts. In addition, it discusses Labov's variation analysis, particularly focusing on his analysis of narrative discourse. After that, this paper shows major topics and methods of conversation analysis, which deals with social actions reflected in talk-in-interaction. It also deals with critical discourse analysis which deals with many social issues, viewing language as a reality-creating social practice. Finally, this paper shows that many approaches to discourse in sociolinguistics have contributed to a better understanding of the roles of social factors reflected in the use of language.