This chapter focuses on the mechanisms of genetic transduction in the Gram-negative bacteria. The major emphasis is on generalized transduction by a variety of bacteriophage, carrying both small and large DNA segments. The fate of the DNA introduced by generalized transduction is discussed, as well as cotransduction analyses and marker effects. The concept of abortive transduction is introduced, as well as the practical uses for generalized transduction. In addition the chapter also discusses specialized transduction and the biology of the bacteriophage lambda. This information supplements the extensive discussion on this subject by Hendrix in this same volume.