Abstract: The subject invention provides a unidirectional site-specific integration system for integrating a nucleic acid into the genome of a target cell. The provided systems include a (1) a mutant, unidirectional site specific integrase, which can be provided by an integrase vector encoding the mutant integrase and (2) a targeting vector that includes: (a) a nucleic acid to be integrated; and (b) a vector attachment site, where the targeting vector attachment site serves as a substrate for the mutant, unidirectional site-specific integrase. In using the subject systems for site-specific integration, the targeting vector and integrase are introduced into the target cell and the cell is maintained under conditions sufficient to provide for site-specific integration of the nucleic acid into the target cell genome via a recombination event mediated by the site-specific integrase. Also provided are kits that include the subject systems.