The present invention provides methods of site-specifically integrating a polynucleotide sequence of interest in a genome of a eucaryotic cell, as well as, enzymes, polypeptides, and a variety of vector constructs useful therefore. In the method, a targeting construct comprises, for example, (i) a first recombination site and a polynucleotide sequence of interest, and (ii) a site-specific recombinase, which are introduced into the cell. The genome of the cell comprises a second recombination site. Recombination between the first and second recombination sites is facilitated by the site-specific recombinase. The invention describes compositions, vectors, and methods of use thereof, for the generation of transgenic cells, tissues, plants, and animals. The compositions, vectors, and methods of the present invention are also useful in gene therapy techniques.