ABSTRACT As a case study in the formation of a new written language in a speech community moving from diglossia toward a “standard-with-dialects”, this article analyzes the development of M[odern] W[ritten] C[hinese] during the past 80 years. After a brief account of the historical background, the article discusses the sources and avenues of influence on the development of MWC, then examines the emergent grammatical and lexical norms, and investigates the variations displayed by the four main Chinese communities: mainland China, Taiwan, Hong Kong, and Singapore. The role of language planning is also explored. The similarities and differences between China and Western Europe, in their progress from diglossic to non-diglossic communities, are discussed. (Diglossia, Chinese linguistics, written language, language planning)