The structural maintenance of chromosomes (SMC) complex, SMC5/6, is important for genome maintenance in all model eukaryotes. To date, the most extensive studies have focused on the roles of Smc5/6 in lower eukaryotes, such as yeast and fly. In the handful of studies that have used mammalian cells, siRNA was used by most to knockdown SMC5/6 components. RNAi methods have been very important for scientific progression, but they are hindered by incomplete silencing of protein expression and off-target effects. This chapter outlines the use of a conditional knockout approach in mouse embryonic fibroblasts to study the function of the SMC5/6 complex. These cell lines provide an alternative method to study the function and properties of the SMC5/6 complex in mammals.