Abstract: Message Sequence Charts (MSCs) have gained wide acceptance for scenario-based specification of component behaviors. MSCs are very useful during requirements capture phase of the software development process and reveal errors in requirement specifications when used in early stages. As MSCs have found widespread usage, there have been several extensions to overcome its' shortcomings for a spectrum of applications keeping the rationale of MSCs invariant. In this paper, we propose a) An extension of hierarchical MSCs (hMSC for short), called MSC+, keeping in view the need of complex reactive system specifications; it has new additional features such as watching (preemptive) construct, generalized coregions, and includes features for the specifications of live and for-bidden scenarios. b) A formal translation of MSC+ to the synchronous language ESTEREL is also provided. This feature enables validating requirement specifications and also to obtain a prototype for synchronous MSC+ specifications. Apart from obtaining a prototype, the translation of MSC+ to ESTEREL (that has clean and mathematical semantics) provides a clear semantic definition for the synchronous MSC+ specifications. In the paper, we shall describe, the design and implementation of MSC+ followed by the translation of MSC+ to ESTEREL leading to prototyping of systems. Examples will be used to highlight characteristic features of the language, system and applications.