This paper motivates the use of a synchronous methodology to program, to verify and to implement real-time applications. The main features of the synchronous language \signal\ are presented and some methodological principles are proposed. \signal\ programming is illustrated through the development of a realistic application, a complex digital watch. Then, an overview of the software environment associated with \signal\ is presented. This environment encompasses formal verification as well as implementation tools to infer reliable real-time implementations on various architectures including distributed ones. All these tools are acting on a unique but polymorphic abstract program representation, namely Synchronous-Flow Dependence Graphs, which provides the \signal\ software design environment with a great homogeneity.