In the last years, DNA arrays have attracted increasing attention among medical diagnosis and analytical chemists. The broad range of application that has been found for DNA arrays makes them an important analytical tool. The main goal of this book is to broadly review the emerging technology of oligonucleotide based biosensors for DNA and protein detection, devoting special attention in target label free electrochemical biosensors. The first two chapters explore the technology behind oligonucleotide and aptamer based biosensors and review the state of the art of these devices. In next chapters, emphasis is laid on the experimental development of biosensors, ranging from bio-self assembled surfaces modification to arrays microfabrication and from electrochemical detections to oligonucleotide label-conjugation. This book provides a useful tool for study thoroughly this emerging field, giving to the reader not only a wide biosensors overview, but also experimental protocols for the development of these devices. This book should be specially useful for researchers in biosensors, electrochemistry detection and bio-surface modification or anyone else interested on this topic.