The investigation of extracellular RNA (exRNA) has gained considerable momentum in recent years, underscoring its critical role in biomarker discovery and the development of innovative cancer therapies. exRNA comprises a diverse array of RNA subpopulations, each playing distinct biological roles. These RNA molecules are protected from enzymatic degradation through encapsulation within membranous vesicles, such as exosomes and microvesicles, or by forming complexes with lipids and proteins. exRNA is ubiquitously present in various biofluids, including blood, urine, saliva, and cerebrospinal fluid, making it an accessible and minimally invasive target for clinical diagnostics. This accessibility is particularly advantageous for cancer detection and monitoring, where non-invasive methods are highly sought after. The ability of exRNA to reflect the physiological and pathological state of cells and tissues positions it as a powerful tool for both diagnostic and prognostic purposes. Recent technological advancements have significantly broadened our understanding of exRNA biology. Key areas of progress include the elucidation of the mechanisms underlying exRNA biogenesis, the processes governing its compartmentalization within cells, and the sophisticated packaging systems that facilitate its incorporation into extracellular vesicles. These insights have paved the way for exploring exRNA not only as biomarkers but also as potential therapeutic agents, given their ability to mediate intercellular communication and influence various biological pathways. Despite these promising developments, several challenges remain in the field. The isolation and purification of exRNA present significant technical hurdles, as achieving high purity and yield is crucial for reliable downstream analyses. Variability in isolation methods can lead to inconsistencies in data, underscoring the need for standardized protocols to ensure reproducibility and accuracy in exRNA research. This chapter delves into the intricate processes involved in exRNA biogenesis, detailing the cellular machinery and pathways responsible for its production and release. We will explore the diverse sources of exRNA, the regulatory mechanisms that govern its expression and secretion, and the various types of extracellular vesicles that serve as carriers. The subsequent chapter will then transition to examining the functional roles of exRNA in human diseases, with a particular emphasis on its utility in diagnostic and therapeutic applications. By providing a comprehensive overview of exRNA biology and its potential clinical implications, we aim to highlight the transformative impact of this emerging field on modern medicine.