Durum wheat (Triticum turgidum L. var durum) is mainly grown in drought-prone areas within the Mediterranean Basin, where terminal stresses, mostly drought and heat, are the major yield constraints. This study was conducted within the framework of the EU-project IDuWUE (Improving Durum wheat for Water Use Efficiency and yield stability through physiological and molecular approaches), in order to ascertain the contribution of yield components and some morpho-physiological traits to explain yield variations in a range of Mediterranean environments. Eight experiments, including a RIL population of 249 lines or a collection of 192 durum wheat accessions, were conducted in contrasting agro-ecological zones within the Mediterranean Basin. Yield, yield components, test weight, flag leaf posture, time from sowing to heading, peduncle length and plant height were measured on each plot. Principal component analysis revealed a wide range of genetic and environmental variability, with the two sets of germplasm showing contrasting phenotypic structure regarding the measured traits. Stepwise regression analysis across environments revealed that yield components accounted for ca. 87.5% of yield variations (grain weight 63.1%, grains per spike an additional 12.5% and spikes per m2 an extra 11.9%). The contribution of morpho-physiological traits to explain yield variations was much lower. Our results reveal that variability in durum wheat yield across Mediterranean environments was mostly due to variability in grain weight.