In this paper, we introduce a wireless web-based ordering system called iMenu in restaurant industry. By using wireless devices such as Personal Digital Assistants (PDAs) and WebPads, this system realizes the paradigm of pervasive computing at tableside. Detailed system requirement, design, implementation and evaluation of iMenu are presented. While many researchers have explored wireless web-based information systems in different industries, this paper presents a system that employs wireless multi-tiered web-based architecture to build pervasive systems. Instead of discussing theoretical issues on pervasive computing, we focus on practical issues of developing a real system, such as choosing of web-based architecture, design of input methods in small screens, and response time in wireless web-based systems. The evaluation of iMenu shows it increases productivity of restaurant staff. It also has other desirable features such as integration, interoperation and scalability. Compared to traditional restaurant ordering process, by using this system customers get faster and better services, restaurant staff cooperate more efficiently with less working mistakes, and enterprise owners thus receive more business profits.