In the last few years, significant advances have been made in the area of gene therapy for both genetic and acquired diseases. Improvement in gene transfer methods has allowed for development of gene therapy protocols for the treatment of diverse types of diseases, including metabolic, cardiovas- lar, and autoimmune diseases, as well as cancer. For example, clinical trials for gene therapy of cancer, cystic fibrosis, ADA deficiency, and arthritis, among others, have been initiated in recent years. It is likely that, in the near future, gene therapy will become a common form of treatment for many different types of diseases. Gene therapy takes advantage of recent advances in many areas of molecular and cell biology, including the identification of new the- peutic genes, improvement in both viral and nonviral gene delivery systems, better understanding of gene regulation, and improvement in cell isolation and transplantation. Because of the different and complex techniques involved in achieving successful gene-mediated therapies, it is difficult for scientists to perform all methods required for gene delivery and subsequent in vivo gene expression. This Gene Therapy Protocols volume in the Methods in Molecular Me- cine series provides scientists with detailed methods for working with gene transfer systems, and methods for gene transfer to specific tissue types either in vivo or ex vivo.