The topic of this thesis is style sheet languages for structured documents on the web. Due to characteristics of the web — including a screen-centric publishing model, a multitude of output devices, uncertain delivery, strong user preferences, and the possibility for later binding between content and style — the hypothesis is that the web calls for different style sheet languages than does traditional electronic publishing. Style sheet languages that were developed and used prior to the web are analyzed and compared with style sheet proposals for the web between 1993-1996. The dissertation describes the design of a web-centric style sheet language known as Cascading Style Sheets (CSS). CSS has several notable features including: cascading, pseudo-classes and pseudo-elements, forward-compatible parsing rules, support for different media types, and a strong emphasis on selectors. Problems in CSS are analyzed, and recommended future research is described.