RNA plays a crucial role in molecular crowding, a phenomenon that significantly impacts the formation, dynamics, and function of protein-RNA assemblies in cells. This review explores the chemical principles governing RNA-mediated crowding events, such as granules or biological condensates. It examines the role of RNA sequence, structure, and chemical modifications in these processes, highlighting their correlation with crowding phenomena under physiological conditions. The review also investigates instances where crowding deviates from its intended function, leading to pathological consequences. By understanding the balance governing molecular crowding driven by RNA and its implications for cellular homeostasis, the review aims to shed light on this area of research. It discusses methodologies used to characterize RNA granules, including computational approaches, and provides examples of noncoding RNAs, NEAT1 and XIST, in the formation of phase-separated assemblies and their influence on cellular function. The review covers the physiological and aberrant phase separation phenomena, offering a multifaceted understanding of RNA-mediated biological condensates. It also explores the impact of enzymatic modifications on RNA molecules, their physical properties, and interactions with other molecules. The review highlights the importance of RNA in cellular organization and function, and its potential impact on pathological conditions such as neurodegeneration and cancer. It discusses the methods used to study RNA crowding, including physical properties of RNA granules, experimental techniques, and structural features of RNA involved in biological condensates. The review provides specific examples related to NEAT1 and XIST, emphasizing their roles in RNA-mediated biological condensation. Overall, the review aims to provide a comprehensive overview of the diverse and multifaceted roles of RNA in health and disease, potentially unlocking new therapeutic avenues.RNA plays a crucial role in molecular crowding, a phenomenon that significantly impacts the formation, dynamics, and function of protein-RNA assemblies in cells. This review explores the chemical principles governing RNA-mediated crowding events, such as granules or biological condensates. It examines the role of RNA sequence, structure, and chemical modifications in these processes, highlighting their correlation with crowding phenomena under physiological conditions. The review also investigates instances where crowding deviates from its intended function, leading to pathological consequences. By understanding the balance governing molecular crowding driven by RNA and its implications for cellular homeostasis, the review aims to shed light on this area of research. It discusses methodologies used to characterize RNA granules, including computational approaches, and provides examples of noncoding RNAs, NEAT1 and XIST, in the formation of phase-separated assemblies and their influence on cellular function. The review covers the physiological and aberrant phase separation phenomena, offering a multifaceted understanding of RNA-mediated biological condensates. It also explores the impact of enzymatic modifications on RNA molecules, their physical properties, and interactions with other molecules. The review highlights the importance of RNA in cellular organization and function, and its potential impact on pathological conditions such as neurodegeneration and cancer. It discusses the methods used to study RNA crowding, including physical properties of RNA granules, experimental techniques, and structural features of RNA involved in biological condensates. The review provides specific examples related to NEAT1 and XIST, emphasizing their roles in RNA-mediated biological condensation. Overall, the review aims to provide a comprehensive overview of the diverse and multifaceted roles of RNA in health and disease, potentially unlocking new therapeutic avenues.