Research on sociolinguistics continues to flourish in the world. There are differences and similarities between Japanese and Korean studies, which influence each other. There are two tendencies in the trends of sociolinguistics: variation and discourse. In this paper, sociolinguistic research topics are positioned in four fields of sociolinguistics. The first field is linguistic relativity, and the second field is description of language variation (languages, dialects, group language, honorifics, etc.). The third field is the description of language performance, which deals with the arrangement of words. The fourth field deals with the performance of language variation. The order from the first field to the fourth field coincides with the historical development of theories over the last 100 years. Based on these four fields, I survey Japanese research and relate it with Korean research. It can be read that Japan and Korea have developed their researches in accordance with the social conditions in their respective countries. This made it possible to see the potential for future development. It is necessary to collect a large amount of data and construct a corpus and publish it. In addition, research combining two major trends in sociolinguistics, variation and discourse is desired, and the future of the fourth field is promising. Theories/methodologies/ research techniques and research target languages can be viewed separately at different levels. Research on Japanese can be applied to other languages as well, which will bring about theoretical development.