While membrane technology is still young and has great potential for further improvements, it has been proven economical and technically efficient in many applications such as treatment of natural gas. In this paper a brief history of membrane gas separation technology is presented, and the theoretical aspects of the process are discussed. The article also introduces applications of membranes in the natural gas industry, discusses different system designs and the effects of operating parameters on the performance of membrane systems, and compares the technical and economical aspects of membrane processes with conventional technologies.