Proteins must be designed for synthesis from genes in plasmids, then optimized for expression and purification, and these processes may be different for each protein and challenging to be optimized. In contrast, RNA can be easily synthesized and purified by established methods using commercially available reagents and equipment. Small RNAs, such as aptamers, siRNAs, miRNAs, and ASOs can be synthesized using solid-support chemistry in commercial oligonucleotide synthesizers. In vitro transcription using commercial kits 120 produces longer RNAs, i.e., mRNAs and lncRNAs. The sequence of the RNA can be changed easily, providing custom molecules targeting different proteins or genes. Thus, the development of RNA therapeutics and vaccines that target disease-specific genes or proteins is relatively fast and straightforward. This was demonstrated by the development, testing, and administration of the COVID-19 mRNA vaccines within a year of the isolation and sequencing of the SARS-CoV-2 viral genome. Most RNAs regulate transcription, post-transcriptional processing, and translation, but they do not alter the genome. The exception is the CRISPR-Cas system in which the guide RNA and Cas endonuclease can edit the genome. RNA aptamers, which mimic ligands, regulate post-translational protein activity. The rapid degradation and predictable pharmacokinetics of RNAs provide them with a safety advantage over gene therapies. Despite the attractiveness of the plug-and-play concept of RNA therapeutic drug design, they require testing to determine their efficacy and safety, and cell delivery is difficult because RNA is easily degraded. The therapeutic RNA must penetrate the cell membrane and escape endosomal entrapment. Although designed for specific targets, therapeutic RNAs can have off-target effects, limiting their usefulness as drugs. Several of these limitations can be mitigated by chemically modifying the RNA to increase target specificity, lower nuclease susceptibility, and improve cellular uptake. The types of RNA in medicine in the development pipeline and their targeted diseases