Microarrays (miniaturized chip-based "laboratories" for studying gene expression) and XML (Extensible Markup Language) are two modern developments that are coming together. Now that whole genomes are available, microarray techniques enable you to measure the relative levels of thousands of gene transcripts at a time, and with their help, we hope to unravel the many pathways and interactions between the genes and gene products in the cell. XML is, to be painfully brief, a kind of new and improved HTML that is emerging as a standard for storing and interchanging data. (This book was written making extensive use of XML.) XML is becoming an important interface to many new kinds of experimental data.