Why RNA and DNA Have Different Structures -- Regulatory RNAs as Mediators of Virulence Gene Expression in Bacteria -- Regulatory RNAs in Mammals -- Aminoglycoside Interactions with RNAs and Nucleases -- High-Throughput RNA Interference in Functional Genomics -- Antiviral Applications of RNAi -- RNA Interference: Its Use as Antiviral Therapy -- Gene Silencing of Virus Replication by RNA Interference -- Progress in the Development of Nucleic Acid Therapeutics -- Screening and Determination of Gene Function Using Randomized Ribozyme and siRNA Libraries -- Ribozymes and siRNAs: From Structure to Preclinical Applications -- Strategies to Identify Potential Therapeutic Target Sites in RNA -- Oligonucleotide-Based Antiviral Strategies -- Gene-Expressed RNA as a Therapeutic: Issues to Consider, Using Ribozymes and Small Hairpin RNA as Specific Examples -- RNA Aptamers: From Basic Science Towards Therapy -- RNA Aptamers Directed Against Oligosaccharides -- Aptamer-Based Biosensors: Biomedical Applications -- Application of Aptamers in Therapeutics and for Small-Molecule Detection -- RNA Aptamers as Potential Pharmaceuticals Against Infections with African Trypanosomes -- RNA Targeting Using Peptide Nucleic Acid -- Locked Nucleic Acid: High-Affinity Targeting of Complementary RNA for RNomics -- Engineering RNA-Based Circuits -- Selection of RNase-Resistant RNAs. Developments over the past few years have revealed the remarkable versatility of RNA in any compartment of the cell, tasks that had been thought to be exclusively in the realm of proteins and even beyond. The chapters in this book written by leading investigators in the field provide insight into various promising avenues where RNA and nucleic acid derivatives including antisense RNAs, such as siRNA, miRNAs, amplification/selection (SELEX) generated aptamers as well as ribozymes are at the threshold of impacting medicine.