Web archiving is an emerging concept whose main purpose is to preserve web-sites of cultural or historical significance. In this paper, we describe the NTU Web Archiving System, NTUWAS, that was developed by the National Taiwan University Library and launched in 2006. In order to help readers not be familiar with web archiving, we give a brief survey of current web archiving activities in the world. We then describe the implementation and functionalities of NTUWAS, as well as the difficulties and problems that we encountered when carrying out this project.