With the growing demand for computing resources and network capacity, providing scalable and reliable computing service on the Internet becomes a challenging problem. Recently, much attention has been paid to the "utility computing" concept that aims to provide computing as a utility service similar to water and electricity. While the concept is very challenging in general, we focus our attention in this chapter to a restrictive environment-Web applications. Given the ubiquitous use of Web applications on the Internet, this environment is rich and important enough to warrant careful research. This chapter describes the approaches and challenges related to the architecture and algorithm design in building such a computing platform.