Various authors have proposed that courtship feeding evolved under natural selection, sexual selection or both. Using observations of 250 breeding pairs over 3 consecutive years for a total of 77 000 nest-hours, we examined the functional significance of courtship feeding in a seabird, the black-legged kittiwake, Rissa triclactyla. We predicted courtship feeding would benefit males and females in different ways: males may invest in future progeny and females may allow copulations in exchange for food or use courtship feeding to assess males' parental quality. Courtship feeding was correlated with clutch size in I of 3 years, suggesting that males may increase their reproductive success by provisioning their mates. Courtship feeding, which was individually repeatable between years, was also related to male arrival date. These results suggest that courtship feeding is a reliable index of male quality that females may use for mate appraisal. Because courtship feeding commences after the pair bond is established, it cannot be used as a criterion for mate choice in the pair's first year. However, courtship feeding rate was related to male re-pairing success in the following breeding season. We thus suggest that courtship feeding in kittiwakes could have first evolved under natural selection (the nutrition hypothesis) and subsequently may have become a signal of mate quality that females could use to evaluate their mates for future seasons (future mate appraisal hypothesis). (C) 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.