DNA microarray technology has become a useful technique in gene expression analysis for the development of new diagnostic tools, and for the identification of disease genes and therapeutic targets for human cancers. Appropriate control for DNA microarray experiments and reliable analysis of the array data are key to performing the assay and utilizing the data correctly. The most difficult challenge has been the lack of a powerful method to simultaneously analyze the data for all human genes (more than 30 000 genes). In this book, DNA microarray technology and data analysis are discussed by pointing out current advantages and disadvantages of the technique as well as the pros and cons of available analytical methods. Based on the editors own experience in DNA microarray studies and analyses, some new ideas and analytical methods are presented.