This book focuses on the fundamentals and applications of messenger RNA (mRNA)-based therapeutics and discusses the strengths and key challenges of this emerging class of drugs. In the past 30 years, extensive research and technological development in many areas have contributed to the emergence of in vitro transcribed mRNA as a therapeutic that has now reached clinical testing. Formulations that protect the mRNA from nucleases and accelerate its cellular uptake, combined with improvements to the mRNA molecules themselves, have been critical advancements for mRNAs to become viable therapeutics. Though once regarded as a serious impediment, the transient nature of mRNA technology is now considered a major advantage in making mRNA therapies safe and, ultimately, a potential game changer in the field of medicine. This new book in the RNA Technologies series provides a state-of-the-art overview on the emerging field of mRNA therapeutics covering essential strategies for formulation, delivery, and application. It also reviews the promising role in cancer immunotherapy, respiratory diseases, and chronic HBV infection and discusses RNA vaccines in light of the current COVID-19 pandemic. mRNA-based approaches have great potential to revolutionize molecular biology, cell biology, biomedical research, and medicine. Thus, this handbook is an essential resource for researchers in academia and industry contributing to the development of this new area of therapeutics.