The field of gene therapy has developed at an astonishing pace over the past decade, perhaps too quickly. Clinical studies have highlighted major flaws in the ability of current vectors to deliver genes safely and effectively to patients; hence the further development of vectors is a prerequisite for future success. In this chapter we have discussed advances in development of targeted vectors through isolation of targeting moieties using phage display. The field of gene therapy will benefit considerably by the isolation and use of peptides that are effective for targeting in vivo, particularly for diseases affecting individual organs. Only when truly selective and highly efficient vectors are constructed will the tremendous potential of gene therapy be realized.