The breeding biology of Grey Wagtails in Ireland was studied over 14 years. A total of 220 nests was located, mostly on bridges. First egg dates varied from 29 March to 2 July with a peak of egg laying in the second week of April. The mean clutch size teas 4.79 (+/- 0.04 se), the mean brood size at hatching 4.59 (+/- 0.05 se) and at fledging 4.00 (+/- 0.09 se) per successful pair. Most clutches (71%) consisted of five eggs, and these hatched and fledged more young than clutches of four. Some data on growth rates of nestlings are presented and some aspects of the breeding biology of the most westerly population of Grey Wagtails are described and compared with other studies.