This text is a comprehensive survey of DNA structure, from first principles to the ways in which drugs and proteins interact with DNA. Such an understanding of DNA structure is essential for more detailed study in areas such as gene regulation and DNA-targeted drug action. It begins by summarizing the major methods used to study DNA structural features, and provides readers with a critical assessment of these methods in practice. It goes on to describe the structural features of DNA at the basic level and then in detail, and then examines non-standard DNA structures. Finally, it describes the principles of DNA-ligand recognition, with water, drugs and protein interactions being covered. Stephen Neidle is the author of "Principles of Nucleic Acid Structure" and "Understanding DNA".