Virus populations are complex ensembles of distinct but related genomes (so called quasi-species). Mathematical descriptions of viral quasi-species focus on point mutations as the principal source of variation. However, retroviruses (and many other viruses) are able to recombine their genomes. We study a mathematical model of viral quasi-species dynamics which incorporates both point mutation and recombination. We show that for low mutation rates recombination can reduce the diversity of the quasi-species and enhance overall fitness. For high mutation rates, however, recombination can push the quasi-species over the error threshold, and thereby cause a loss of all genetic information. Finally, recombination introduces bistability to the quasi-species; if the frequency of an advantageous mutant is below a certain threshold, it will not be selected.