Transfection (i.e., delivery) of genes, RNA, or proteins into cells is a foundational technique in the life sciences. Successful transfection is critical for a range of applications, including studies of gene expression, gene knockdown (i.e., RNAi), genome editing, and protein expression for biopharmaceuticals. Furthermore, advances in mammalian cell transfection technologies, such as in vivo delivery, have proven invaluable to clinical research, with these techniques playing pivotal roles in the development of vaccines as well as cell and gene therapies.