Abstract An essential step to assure the proper long-term performance of a geomembrane liner that is in the process of being installed is 100% inspection of the seams to ensure their continuity. This step must be complemented with destructive testing of the seams to ensure their strength and integrity. At the present time, the principal destructive tests of seams involve strategic sampling and testing of the seams in accordance with standard ASTM methods for seam strength in shear and peel modes. This paper describes the seam testing of the different types of geomembranes and discusses specific tests that are used. Also discussed are the variables that are involved in the testing and the requirements that should be stated in the specifications in order to assure full understanding of the acceptance criteria and the requirements of quality control and quality assurance. The results of testing current geomembranes are presented. Finally, some limitations of destructive testing of seams are discussed.