Genome sequences are now available that enable us to determine the biological components that make up a cell or an organism. The new discipline of systems biology examines how these components interact and form networks, and how the networks generate whole cell functions corresponding to observable phenotypes. This textbook describes how to model networks, determine their properties, and relate these to phenotypic functions. Some knowledge of linear algebra and biochemistry is required, since the book reflects the irreversible trend of increasing mathematical content in biology education.