This book describes the development of novel protein–RNA-binding assays and their applications in a high-throughput manner for the identification of small-molecule modulators of protein–RNA interactions to treat cancer and COVID-19. Modulating protein–RNA interactions with small molecules is expected to provide novel biological insights of the interrelation of diseases with the protein–RNA interactome. The modulations may also be exploited therapeutically. For these reasons, the development of a simple, reliable, and sensitive protein–RNA-binding assay is necessary for high-throughput screening to discover new effective chemical entities capable of acting on diverse protein–RNA interactions. This book discusses the discovery of small-molecule modulators targeting protein–RNA interactions that are potentially valuable to treat cancer and COVID-19 by constructing novel high-throughput screening methods. The results of this dissertation provide valuable insights into the regulation of protein–RNA interactions in chemical biology and drug development.