Abstract : We start this chapter by explaining how modeling needs of thereal-time community have lead to the introduction of synchronouslanguages in the early 1980s. We present the characteristics of theselanguages as well as their limitations. We then propose aclassification of synchronous languages and of the languages relatedto them. This introduces a description of the main synchronouslanguages Signal, Lustre and Esterel byhighlighting their similarities and differences. We follow bydescribing the main techniques which allow to perform real-timescheduling from these synchronous languages. Finally, we present a fewextensions of these languages allowing to perform real-time schedulingmore easily.