A collection of 154 durum wheat landraces from 20 Mediterranean countries and 18 modern varieties was used to examine the existing variability for the main quality traits and to identify potential quality-enhancing genotypes for use in breeding programs. Field experiments were conducted during 3 years under rainfed conditions in north-eastern Spain. Based on yield and quality attributes, landraces were clustered according to their region of origin in eastern Mediterranean, western Mediterranean, and North-Balkan Peninsula. Landraces from the eastern Mediterranean countries had the highest global quality and the widest variability for quality traits, but were characterized by relatively small grains. Landraces from the western Mediterranean countries had the heavier grains, while landraces from the North-Balkan Peninsula had low quality and small quality variability. Modern varieties showed the highest global quality, but they had the lowest grain protein content and phenotypic variability. The assessment of the allelic composition at five glutenin loci (Glu-A1, Glu-B1, Glu-A3, Glu-B3, and Glu-B2) allowed identifying 114 alleles/banding patterns in the collection. Three rare banding patterns, found on a few number of landraces, affected significantly gluten strength. Landraces with improved quality traits, particularly gluten strength and grain weight were identified as potential donors for quality improvement.