The development of in vitro transposition technologies have provided many powerful tools for the molecular genetics research laboratory. In this chapter we describe some of these tools with a focus on the Tn5 transposition system. Tn5 technologies are particularly useful because the Tn5 transposition system has simple requirements, is efficient, random in target recognition, and robust. In particular we will describe the use of in vitro Tn5 transposition in transposon tagging and in the generation of nested deletions. We will also describe a unique in vitro/in vivo technology in which Tn5 inserts can be generated in a wide spectrum of bacterial species through the electroporation of preformed tranposase-transposon DNA complexes.