Abstract
This chapter discusses formal methods, which consist of a set of mathematic techniques that provide an extra level of confidence in the correctness of the software. They consist of a formal specification language and employ a collection of tools to support the syntax checking of the specification, as well as the proof of properties of the specification. They allow questions to be asked about what the system does independently of the implementation, and they may be employed to formally state the requirements of the proposed system and to derive a program from its mathematical specification. They may be employed to provide a rigorous proof that the implemented program satisfies its specification, and they have been applied mainly to the safety-critical field.