The formulation and the technological advancements in RNA biology, chemistry, stability, and encapsulated delivery systems that have enabled the development of fully synthetic mRNA vaccines are discussed in this volume. The applications of the mRNA technology is covered, focusing on infectious diseases but also touching on other indications, such as immunotherapies and molecular therapies. Potent and long-lasting immune responses observed in animal models, encouraging data from early human clinical studies, together with the success of two mRNA-based COVID-19 vaccines support the use of mRNA-based vaccination as an attractive alternative to conventional vaccine approaches. Consequently, the development progress of the technology, particularly on production, capabilities, and clinical development is reviewed. Topics on safety, regulatory issues, and possible challenges to the mRNA vaccination approach round off this book. Thanks to their high potency, the prospect for generic, low-cost manufacturing processes, and entirely synthetic nature, the future for mRNA vaccines is highly promising. Importantly, mRNA vaccines have the potential to minimize the time between pathogen identification and vaccine release with a huge impact on public health.