A notation and methodology for writing formal specifications, based on the Vienna Definition Method developed at the IBM Laboratory in Vienna in the 1960s for the definition of programming languages. See constructive specification.

Three dialects of the formal language of VDM are now in use, and are commonly known as VDM languages: VDM-SL (VDM-Specification Language) is a formal specification language for sequential systems, with support for modular structuring; VDM++ extends VDM-SL with features for object-oriented systems and concurrency, and VDM-RT (VDM-Real Time) extends VDM++ to model real-time embedded and distributed systems. VDM-SL has been standardized by ISO (ISO/IEC 13817-1).