Numerous viral vectors have been developed for the delivery of transgenes to 
specific target cells. For persistent transgene expression, vectors based on 
retroviruses are attractive delivery vehicles because of their ability to stably 
integrate their DNA into the host cell genome. Initially, vectors based on 
simple retroviruses were the vector of choice for such applications. However, 
these vectors can only transduce actively dividing cells. Therefore, much 
interest has turned to retroviral vectors based on the lentivirus genus because 
of their ability to transduce both dividing and non-dividing cells. The best 
characterized lentiviral vectors are derived from the human immunodeficiency 
virus type 1 (HIV-1). This chapter describes the basic features of the HIV-1 
replication cycle and the many improvements reported for the lentiviral vector 
systems to increase the safety and efficiency. We also provide practical 
information on the production of HIV-1 derived lentiviral vectors, the cell 
transduction protocol and a method to determine the transduction titers of a 
lentiviral vector.