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.