Targeted infection of therapeutically attractive cell lines, such as stem cells and astrocytes, remains a significant challenge in gene delivery. Attempts to use natural variants of viral vectors have met with limited success, likely because nature never intended viruses to function as a gene delivery vectors. For instance, adeno-associated viral (AAV) vectors have proven to be safe and efficient gene delivery vectors. Previous rational design approaches to design AAV variants has generated vectors with some cell selective gene delivery properties. However, refractory cell types may possess more than one rate limiting step, dramatically reducing the success of these methods, and lack of extensive structure/function knowledge of many AAV variants further restricts the use of rational approaches. Furthermore, AAV2 binds heparan sulfate proteoglycans (HSPGs) as its cell surface receptor, but many cell lines lack significant levels of HSPGs to allow for the binding of AAV vectors. The AAV capsid structure is a major determinant of its gene delivery properties, and we have therefore developed novel approaches to engineer the capsid proteins. Specifically, the creation of several large diverse AAV2 libraries, through recombination and mutagenesis, has allowed us to select novel AAV virions with desired phenotypes. Initial characterization of these libraries indicates they contain variants with novel cellular tropisms. Further rounds of evolution of these vectors will allow for the engineering of a customized gene deliver vehicle.