This review discusses the use of circular dichroism (CD) spectroscopy to study the conformational properties of DNA. CD spectroscopy is a sensitive and relatively inexpensive method that can be used to analyze DNA samples at various concentrations and lengths. It is particularly useful for studying the B-family of structures, including the A-form, Z-form, guanine quadruplexes, cytosine quadruplexes, triplexes, and other less characterized structures. CD spectroscopy can distinguish between gradual changes within a single DNA conformation and cooperative isomerizations between different structural states, allowing for the measurement of kinetic and thermodynamic parameters. The review highlights the advantages of CD spectroscopy over other methods, such as X-ray crystallography and NMR spectroscopy, and its role in the discovery of key DNA structures and their functions. The article also covers specific examples of DNA conformations, such as the B-form, A-form, Z-form, and various quadruplexes, and discusses the transitions between these conformations. Additionally, it explores the relationship between solution and crystal conformations of DNA and the potential applications of CD spectroscopy in drug design and gene regulation.This review discusses the use of circular dichroism (CD) spectroscopy to study the conformational properties of DNA. CD spectroscopy is a sensitive and relatively inexpensive method that can be used to analyze DNA samples at various concentrations and lengths. It is particularly useful for studying the B-family of structures, including the A-form, Z-form, guanine quadruplexes, cytosine quadruplexes, triplexes, and other less characterized structures. CD spectroscopy can distinguish between gradual changes within a single DNA conformation and cooperative isomerizations between different structural states, allowing for the measurement of kinetic and thermodynamic parameters. The review highlights the advantages of CD spectroscopy over other methods, such as X-ray crystallography and NMR spectroscopy, and its role in the discovery of key DNA structures and their functions. The article also covers specific examples of DNA conformations, such as the B-form, A-form, Z-form, and various quadruplexes, and discusses the transitions between these conformations. Additionally, it explores the relationship between solution and crystal conformations of DNA and the potential applications of CD spectroscopy in drug design and gene regulation.