This document discusses formal specification techniques for software. It describes algebraic techniques for specifying interfaces as abstract data types and model-based techniques for specifying system behavior. Algebraic specifications define operations and their relationships, while model-based specifications represent the system state using mathematical constructs like sets and sequences. Formal specification finds errors earlier and reduces rework, though it requires more upfront effort. The document also provides an example of formally specifying an air traffic control system and insulin pump.