Nanostructures, with their localized interactions with mammalian cells, can offer better efficiency and lower cell perturbation than conventional viral, biochemical, and electroporation transfection techniques. In this Perspective, I describe the different stages of transfection and provide a comparison of transfection techniques based on their mechanisms. Focusing on specific aims of transfection, I also illustrate how recent developments in high-aspect-ratio nanostructures have endowed them with properties that are superior to existing viral, biochemical, and electroporation methods as a versatile technique to deliver a variety of cargoes and to interface with different mammalian cell types for biomedical applications. Finally, I describe the challenges associated with transfection that need to be overcome to enhance cargo delivery efficiency and clinical translation.