This book is an introduction to the new field of proteomics. It is intended to describe how proteins and proteomes can be analyzed and studied. Despite widespread, growing interest in proteomics, an understanding of proteomics tools and technologies is only slowly penetrating the research community at large. This book addresses the need to introduce biologists to new tools and approaches, and is for both students of biology and experienced, practicing biologists. Anyone who has taken a graduate level biochemistry course should be able to take from this book a reasonable understanding of what proteomics is all about and how it is practiced. The experienced biologist should encounter much here that is familiar, but refocused to facilitate studies of the proteome. The achievement of long-sought milestones in genome sequencing, analytical instrumentation, computing power, and user-friendly software tools has irrevocably changed the practice of biology. After years of studying the individual components of living systems, we can now study the systems themselves in comprehensive scope and in exquisite molecular detail. We therefore face the tasks of effectively employing new technologies, of dealing with mountains of data, and, most important, of adjusting our thinking to understand complex systems as opposed to their individual components.