Since the discovery of the structure of the DNA double helix in 1953, we know that DNA is of critical importance, carrying the genetic information for all living organisms. Only a few years later the first reports on the chemical synthesis of oligonucleotides appeared. During the past years the field of nucleic acid chemistry has expanded dramatically: natural and artificial functionalities, as well as probes, markers or other biologically active molecules, can be synthetically introduced into DNA (as well as RNA) by preparing the corresponding artificial DNA and RNA building blocks. Although nucleic acid chemistry appears to be a mature part of organic and bioorganic chemistry, the many questions that are still being raised give sufficient motivation to continue to synthesize new nucleic acid probes. Moreover, in addition to their biological functionality, DNA and RNA are considered as increasingly important architectures and scaffolds for two- and three-dimensional objects, networks and materials for nanosciences.