Rhabdomyosarcoma is the most common soft tissue sarcoma of childhood and adolescence. Historically, rhabdomyosarcoma has been studied by the manipulation of human cell lines derived from primary rhabdomyosarcoma tumor tissue adapted to grow in culture. Recently, mouse models have been added to the arsenal of tools to study this disease in vivo. However, given the emerging understanding of the genetic variability and mutability of human tumor-derived cell lines, and the existing differences between human and murine tumorigenesis, we sought to uniformly dissect the genetic events required to generate rhabdomyosarcoma from primary human skeletal muscle precursors. To this end, primary human skeletal muscle cells were transformed with defined genetic elements to corrupt the p53, Rb, Myc, telomerase, and Ras pathways, resulting in cells that, when assayed as subcutaneous xenografts in immunocompromised mice, formed tumors indistinguishable at the immunohistochemical level from the embryonal histologic variant of rhabdomyosarcoma. This chapter will discuss the techniques used to transform primary human skeletal muscle cells, the assays used to verify expression of the ectopically expressed genetic elements, and the methods used to evaluate the tumorigenic capacity of the resulting cell lines.