Drought-tolerant cocksfoot cultivars capable of exploiting off-season moisture could be useful for the Mediterranean region. This study aimed to assess drought tolerance and responsiveness to summer irrigation in 2 sets of materials, namely, 8 populations including Mediterranean and non-Mediterranean ssp. glomerata cultivars and 2 Mediterranean ssp. hispanica natural populations, and 28 half-sib progenies issued by previous phenotypic selection of Mediterranean parent germplasm under summer irrigation. Dry matter (DM) yield under rainfed and summer-irrigated conditions was observed in summer and the following cool season and it was related to plant survival at the end of summer, concentration of soluble sugars and total nitrogen before and at full imposition of the summer treatments, and leaf-extension rate at early treatment imposition. The results indicated that: (i) a complete vegetative arrest under stress is a prerequisite for summer survival in Mediterranean environments; (ii) selected Mediterranean material may exhibit a level of responsiveness to moisture availability in summer that is comparable, in some cases, with that of non-Mediterranean germplasm; (iii) responsiveness to summer irrigation may not exert a detrimental effect on the subsequent cool-season regrowth in selected Mediterranean germplasm, whereas a detrimental effect is evident in unselected ssp. hispanica material; (iv) DM yield responses under rainfed and irrigated conditions are genetically compatible, as shown by the moderate positive genetic correlation (r_g = 0.51); (v) the selection for responsiveness to summer irrigation in Mediterranean germplasm of ssp. glomerata or ssp. hispanica can be effective; and (vi) Mediterranean germplasm accumulates soluble sugars during the dry period, but the value of this or other physiological traits as an indirect selection criterion within adapted Mediterranean germplasm is questionable.