Requirements validation makes sure that the requirements written in software requirements specification (SRS) must be complete and consistent and are according to the customer's needs. It ensures the validity of user requirements by eliminating ambiguities and inconsistencies from SRS. Several techniques for requirements validation have been discussed in the literature. This paper gives an overview of requirements validation techniques which have been practicing in industry, which includes requirements inspections, requirements prototyping, requirements testing and viewpoint-oriented requirements validation. This paper also highlights pros and cons of these techniques. In requirements testing, special attention is given to TCD inspections.