During the last 10 years and in particularly within the last few years, there has been a data explosion associated with the completion of the human genome project (HGP) (IHGMC and Venter et al., 2001) in 2001 and the many sophisticated genomics technologies. The human genome (and genome from other species) now provides an enormous amount of data waiting to be transformed into useful information and scientific knowledge. The availability of genome sequence data also sparks the development of many new technology platforms. Among the available different technology platforms, microarray is one of the technologies that is becoming more and more mature and has been widely used as a tool for scientific discovery. The major application of microarray is for simultaneously measuring the expression level of thousands of genes in the cell. It has been widely used in drug discovery and starts to impact the drug development process.