INTRODUCTIONModern cell biology increasingly relies on molecular tools to facilitate the study of cellular processes. With the advent of recombinant DNA technology, reverse transcription–polymerase chain reaction (RT-PCR) to amplify almost any gene, and fluorescent proteins that can be fused to any desired target protein, the number and scope of functional studies designed to determine the roles of proteins within cells have exploded. Creating the appropriate fusion protein plasmid is a key step, but the DNA must also be delivered to the cell for expression and function studies. There are several common approaches for delivering DNA, including liposome- and polymer-mediated transfection, electroporation, and direct DNA delivery by microinjection. This article provides an overview of several of these nonviral gene delivery methods, with an emphasis on direct injection of plasmids into cells.