Book excerpt: Driven by rapid developments in protein and DNA sequencing technologies, systems biology has become an important research paradigm. It is marked by an emphasis on integrating data on multiple scales and creating a framework for developing predictive models that are valid across the spectrum of structural hierarchies found in biological systems. This book consists of fourteen original chapters and an introduction that together provide a comprehensive introduction to the subject starting from discussions of its definition and scope and ending in detailed reviews of how the systems approach is affecting clinical research and practice. Most chapters are written to be accessible to a wide readership and contain references to the latest research. Altogether, this is a state-of-the-art description of the present and future of systems biology.