Aegilops longissima is an annual grass species that is native to the eastern Mediterranean Basin and is recognized as a potential source of genetic diversity for cultivated wheat improvement. The primary objectives of this research were to assemble a diverse collection of Ae. longissima and characterize it for agro-morphological traits and resistance to the diseases of stem rust (caused by P. graminis f. sp. tritici), leaf rust (P. triticina) and stripe rust (P. striiformis f. sp. tritici). A collection of 433 accessions of the species, mostly from Israel, was assembled for this study. Evaluation results indicate that Ae. longissima is very diverse for many agro-morphological traits, especially leaf area. With respect to stem rust resistance, 18% and 80% of accessions were resistant to P. graminis f. sp. tritici pathotypes TTTTF and TTKSK, respectively. The percentage of accessions exhibiting resistance to pathotypes of the leaf rust and stripe rust pathogens ranged from 50 to 62%. Ten accessions were resistant to all races of the three pathogens investigated in this study. The great advances made recently in genomics opens up the possibility for exploiting the allelic diversity of Ae. longissima for cultivated wheat improvement.