Oligonucleotide-based diagnostics and therapeutics are attracting attention from the scientific community. In recent years, the range of applications for oligonucleotides has broadened in innovative and creative directions, such as disease diagnostics, cancer prognosis and more. It played an important role during the COVID pandemic in rapid PCR testing as well as modified mRNA-based life-saving vaccines. Various modifications of natural nucleotide bases have been evaluated for several theranostic applications. The development of nucleotide and oligonucleotide therapeutics has been growing in importance over the past few decades. This book examines new developments in oligonucleotide-based research and provides a comprehensive overview of the state of the art in this exciting discipline.