Reverse genetics is gaining importance in the field of modern biological sciences. Gene disruption and the use of siRNAs are the favored techniques for current research. Many researchers, however, are aware that the data from siRNA experiments are frequently inconsistent and that epistatic analysis of multiple genes using siRNAs is barely feasible. In recognition of the drawbacks of the siRNA technique, many researchers, especially in the field of DNA repair, are now introducing multiple genetic disruption techniques using the chicken DT40 cell line into their research. Thus, recent publications increasingly include data utilizing DT40 cells. In this chapter, we describe the current standard methods of multiple genetic manipulation in DT40 cells. We place a particular emphasis on describing the basic concepts and theoretical background of the genetic manipulation of DT40 cells for researchers who are new to such techniques. © 2014 Springer Science+Business Media, LLC.