Reactivity on the Web is an emerging issue. The capability to automatically react to events (such as updates to Web resources) is essential for both Web services and Semantic Web systems. Such systems need to have the capability to detect and react to complex, real life situations. This presentation gives flavours of the high-level language XChange, for programming reactive behaviour on the Web. Categories and Subject Descriptors D.3.3 [Software]: Programming Languages--Language Constructs and Features Keywords Web, reactive languages, event-condition-action rules, composite events