Nucleolin protein is involved in a plethora of cellular pathways across the nucleolus, nucleus, and cytoplasm. The association of its RNA-binding domain (RBD) and its RGG (arginine–glycine–glycine-rich) domain allows it to interact with G-quadruplex structures in nucleic acids. We highlight evidence that the nucleolin/G-quadruplex partnership is of extensive relevance to neurodegenerative disease, cancer, and viral infections. Nucleolin protein is involved in a plethora of cellular pathways across the nucleolus, nucleus, and cytoplasm. The association of its RNA-binding domain (RBD) and its RGG (arginine–glycine–glycine-rich) domain allows it to interact with G-quadruplex structures in nucleic acids. We highlight evidence that the nucleolin/G-quadruplex partnership is of extensive relevance to neurodegenerative disease, cancer, and viral infections.