The notion of silence must be handled very carefully. In addition, its use reveals the way we deal with the urban environment as well as social life. What does the notion of silence convey about the current state of the urban sonic environment? How can we clarify the various meanings and the stakes involved in silence? Three themes are developed in order to answer these questions: silence as a research topic presents three complementary perspectives (acoustic, sociocultural, technological); silence as a polysemous notion emphasises the ideas of keeping quiet, tranquillity and pause; silence as a design issue relies on basic properties and principles in order to orient the design of the urban sonic environment.