The productive phase of human papillomavirus (HPV) infection is dependent on squamous differentiation of epithelial keratinocytes. Organotypic culture systems of primary human keratinocytes (PHKs) or immortalized keratinocytes that contain HPV genomes were developed to recapitulate this permissive environment. A complementary approach to determine the functions of individual HPV genes and to examine the virus-host interactions is to introduce the gene, alone or in combination, into keratinocytes that are then grown in organotypic cultures. The success of the latter approach depends on the methodology of retrovirus-mediated gene transfer, which can transduce the viral gene or genes into an entire population of PHKs. In this chapter, we describe the strategies and methods of retrovirus-mediated gene transfer into keratinocytes grown into organotypic cultures.