The need for uncovering molecular mechanisms in endothelial cell biology has tremendously increased in the last decades as it became more and more clear that the endothelium is an important target in nearly all diseases and treatments (drug delivery) and plays a central role in regeneration processes. One of the critical methods generally applied in cell biology research to uncover structural and functional aspects is the modulation of protein expression by over-expression, expression of mutant variants or gene silencing. This strategy, however, requires genetic manipulation of the respective cells. The classical gene transfer by chemical transfection techniques works pretty well in a large variety of cultured cells but fails for most endothelial cell types. Insufficient transfection rates and gene expression levels as well as the sensitivity of the endothelium against chemical transfection reagents limits utilisation of this technique for endothelial cell biology research. This holds true not only for primary endothelial cell cultures and endothelial cells in vivo but also for endothelial cell lines, e.g. endothelioma cells. The development of viral vectors originally designed for gene therapy approaches has significantly improved the methodological spectrum in endothelial cell research. Two viral vector systems, based on retroviruses and adenoviruses, deliver transgenic information highly efficient into both cultured endothelial cells and in endothelial cells in vivo, respectively. This review aims to give a comprehensive overview of these two vector systems that appear to be reliable and efficient tools for gene delivery into endothelial cell types.