AbstractRNA capping is an essential trigger for protein translation in eukaryotic cells. Many viruses have evolved various strategies for initiating the translation of viral genes and generating progeny virions in infected cells via synthesizing cap structure or stealing the RNA cap from nascent host messenger ribonucleotide acid (mRNA). In addition to protein translation, a new understanding of the role of the RNA cap in antiviral innate immunity has advanced the field of mRNA synthesis in vitro and therapeutic applications. Recent studies on these viral RNA capping systems have revealed startlingly diverse ways and molecular machinery. A comprehensive understanding of how viruses accomplish the RNA capping in infected cells is pivotal for designing effective broad‐spectrum antiviral therapies. Here we systematically review the contemporary insights into the RNA‐capping mechanisms employed by viruses causing human and animal infectious diseases, while also highlighting its impact on host antiviral innate immune response. The therapeutic applications of targeting RNA capping against viral infections and the development of RNA‐capping inhibitors are also summarized.