This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book concentrates on forensic science in the service of criminal law, which is science applied to criminal cases. It emphasizes applications to criminal cases, the application of science to other types of legal concerns is largely analogous. Forensic science generally served to confirm identifications and the nature of well-defined evidence items. Forensic science is, in fact, an incredibly broad subject that people now use to cover virtually any scientific, and some technical endeavors, which have applications to the law. Forensic science laboratories, as we know them today, began to emerge in the early twentieth century. In Europe, they tended to grow out of the medico-legal institutes, which performed what we now think of as primarily forensic pathology functions. Forensic science, in the broad sense of the term, encompasses many different scientific and technological specialty areas.