In view of the complexity and widespread use of Recommendations, it is imperative that adequate and appropriate description techniques and languages be used to ensure the required quality levels of Recommendations. The purpose of this Recommendation is to guide the use of formal description techniques (FDTs) to ensure the quality of ITU-T Recommendations. Where special requirements for verification and validation exist, FDTs should be used. The effective use of FDTs requires phased procedures to introduce their use. This Recommendation states the procedures to accomplish this task. Effective use of FDTs implies the use of state-of-the-art tools.