This textbook presents information on the fundamental properties of nucleic acids and presents modern methods for their study and application. The purpose of this textbook is to introduce undergraduate and graduate students specializing in the chemistry of natural compounds to the most important areas of nucleic acid chemistry: the structure and properties of their individual components, the synthesis of natural and modified oligonucleotides, the basic techniques for sequencing nucleotides in DNA and RNA, the study of their spatial structure, chemical approaches to the study of nucleic acid-protein complexes, and diagnostic methods for diseases associated with genomic damage.