Circular RNAs (circRNAs) are a unique class of single-stranded RNAs characterized by their covalently closed-loop structures. Unlike linear RNAs, circRNAs lack 3′ and 5′ ends, which makes them exceptionally stable and resistant to degradation by exonucleases. This intrinsic stability has garnered significant interest in circRNAs as potential candidates for novel therapeutic applications, including vaccine development. Remarkably, certain circRNAs possess specific structural features that enable them to be translated into proteins, further enhancing their potential utility in vaccine design. Vaccines are powerful tools in immunotherapy, playing a crucial role in the prevention of infectious diseases and the treatment of cancers. The advent of circRNA vaccines represents an exciting new frontier in this domain. Recent advancements have seen the successful synthesis and testing of several circRNA vaccines both in vitro and in vivo, showcasing their promise in eliciting robust immune responses. This chapter provides a comprehensive overview of the current understanding of translatable circRNAs, delving into their biology and functional mechanisms. We explore the molecular biology underlying circRNA formation, the various synthetic methods employed to generate circRNAs, and the strategies for their effective delivery. Additionally, we examine the current landscape of circRNA vaccines, highlighting recent developments and experimental results. Furthermore, we discuss the challenges that need to be addressed to advance the field of circRNA vaccines. These include optimizing circRNA synthesis and delivery, ensuring consistent and efficient translation, and understanding the long-term effects and safety of circRNA-based immunizations. By summarizing the progress made in recent years, we aim to outline the future directions for research and development in this promising area of vaccine technology.