Lentiviral expression vectors are the most effective tools for transducing and stably expressing different effector molecules (cDNA, DNA fragments, siRNA, antisense, ribozymes, etc.) or reporter constructs in virtually any mammalian cell, including nondividing cells and whole model organisms. Like standard plasmid vectors, it is able to introduce lentiviral constructs in plasmid form into the cells with low-to-medium efficiency and get transient expression of effectors by conventional transfection protocols. Through packaging the lentiviral expression construct into pseudoviral particles, we can obtain highly efficient transduction, even with the most difficult to transfect cells, such as primary, stem, and differentiated cells.