Lentiviral vectors are the workhorses of modern cell biology. They can infect a wide variety of cells including non-dividing cells and stem cells. They integrate into the genome of infected cells leading to stable expression. It is easy to transduce 100% of the cells in a culture and possible to infect cells simultaneously with multiple vectors, greatly facilitating studies on malignant transformation. We present simple protocols to produce and titrate lentiviral vectors, infect mammary epithelial cells, and check for contamination with replication competent viruses.