Temperature is one of many important environmental variables that can impact the long-term performance, strength, and deformation characteristics of many man-made construction materials, including geosynthetics. The functional engineering properties of these materials must remain within acceptable limits during their service life to ensure that the overall design and performance are acceptable. In the case of geosynthetics used in landfills and other applications, laboratory interface shear tests are performed under standard test conditions, including temperature. Information emerging today shows that geosynthetic interfaces (i.e., in landfill liner applications) experience elevated temperatures resulting from exothermic reactions occurring in the waste body, amongst other factors. To this end, the field conditions at elevated temperatures should also be simulated in the laboratory during physical/mechanical laboratory tests in order for researchers to better understand in situ functional engineering properties and operational performance of manmade geo-construction materials. For this purpose, a temperature-controlled chamber was designed and developed to allow the shear behavior of geosynthetic geosynthetic and soil geosynthetic interfaces to be evaluated at different temperatures. This paper describes both the development and the validation of the test system. The results of experimental investigations are presented to illustrate how the shear behavior of interfaces between nonwoven polypropylene geotextile and smooth and/or textured high density polyethylene geomembrane, as well as those between rounded and/or angular sand and geomembranes, change with temperature. The results provide insight into the importance of being able to independently control this variable during mechanical testing in the laboratory.