On the occasion of the 20th anniversary of the founding of the Sociolinguistic Society of Korea (SSK), the paper presents a brief retrospective aspect of the developmental history of SSK and a comprehensive overview of the Labovian theory of language variation and change. He is the first sociolinguist who introduced the quantitative method to analyze the linguistic variation. His Master’s thesis Martha’s Vineyard Study (1963) and his doctoral dissertation The Social Stratification of New York English (1964) indeed gave rise to the rapid development of sociolinguistics in late 60s as a counterforce to the popular activities of the theoretical linguistics. Labov’s efforts for the education of the low-income children in Reading also deserve to be included just as great contributions as his linguistic achievements. The three volumes of his Principles of Linguistic Change which have just been completed this year together with The Atlas of North American English which includes vowel changes and chain shiftings of 332 northern American cities to establish the phonology of North American English more or less sum up his life-time achievements of 50 years in research and teaching.