Quadruplex DNA structures, formed from G-rich sequences, have been studied extensively, revealing their potential roles in biology and as therapeutic targets. These structures, composed of G-tetrads, can form in telomeric and non-telomeric regions of DNA, with varying topologies and sequences. High-resolution techniques like X-ray crystallography and NMR have provided detailed structural insights, highlighting the diversity of quadruplex forms. These structures are influenced by factors such as loop length, sequence, and cation type, with Na⁺, K⁺, and other ions playing key roles in stability and conformation. Quadruplexes can be unimolecular, bimolecular, or tetramolecular, with distinct topologies such as parallel, anti-parallel, and diagonal loops. The study of quadruplexes in telomeres and other genomic regions has revealed their prevalence and potential functional significance, particularly in gene regulation and disease. Non-telomeric quadruplexes, found in promoters, gene deserts, and other regions, are also significant, with some sequences showing high frequency and potential for therapeutic targeting. The structural diversity of quadruplexes, including their stability and conformational flexibility, underscores their importance in biological processes and drug development. Further research is needed to fully understand their roles and to develop effective therapeutic strategies.Quadruplex DNA structures, formed from G-rich sequences, have been studied extensively, revealing their potential roles in biology and as therapeutic targets. These structures, composed of G-tetrads, can form in telomeric and non-telomeric regions of DNA, with varying topologies and sequences. High-resolution techniques like X-ray crystallography and NMR have provided detailed structural insights, highlighting the diversity of quadruplex forms. These structures are influenced by factors such as loop length, sequence, and cation type, with Na⁺, K⁺, and other ions playing key roles in stability and conformation. Quadruplexes can be unimolecular, bimolecular, or tetramolecular, with distinct topologies such as parallel, anti-parallel, and diagonal loops. The study of quadruplexes in telomeres and other genomic regions has revealed their prevalence and potential functional significance, particularly in gene regulation and disease. Non-telomeric quadruplexes, found in promoters, gene deserts, and other regions, are also significant, with some sequences showing high frequency and potential for therapeutic targeting. The structural diversity of quadruplexes, including their stability and conformational flexibility, underscores their importance in biological processes and drug development. Further research is needed to fully understand their roles and to develop effective therapeutic strategies.