Lotus corniculatus L. (Legtuninosae), is a perennial herb common throughout Britain. Its main pollinators are bumblebees (Bombus spp., Apidae: Hymenoptera). This is a study of the ecological factors which are important to flowering and fruiting in the species, and some of their evolutionary implications. The work was carried out at Wytham Estate, Oxfordshire, U.K., mainly in an ex-arable field (Upper Seeds) and a more established grassland (Lower Seeds Reserve). The literature on self-incompatibility in L. corniculatus is reviewed; there are conflicting reports, but wild material is fundamentally self-incompatible. Plants in Upper Seeds are larger than in Lower Seeds Reserve. Comparative data on soil nutrients in the two sites suggests that the cause is the persistence of phosphorus from inorganic fertiliser. There is a positive, linear relationship between plant size, flower production and fruit production. The species regulates investment in flowers mainly at the level of the whole inflorescence, rather than altering number of flowers per inflorescence. Within individuals, there are no consistent trade-offs between number of fruit per infructescence, numbers of seeds per fruit and seed weight. Weather patterns only partially explain the flowering phenology of L. corniculatus. Timing of first flowering and peak flowering are correlated but are variable between individuals, and between years for the same individuals. They are not correlated with flowering synchrony. An individual's flowering pattern does not consistently affect fruit-set; the overriding determinant of fruit production is plant size. Selection is therefore unlikely to be acting on flowering time in this species. The production of large numbers of self-incompatible flowers does not seem to reduce fruit-set; pollinators do not visit enough flowers per foraging trip (perhaps because nectar production is low) for geitonogamy to become a problem. Seed predation by larvae of a chalcid wasp, a weevil and a moth differs between individual plants, but not consistently so between years. Seed predation is not consistently correlated with plant size, mean flowers per inflorescence, number of seeds per fruit or seed size. There is no evidence for selection acting on these traits through seed predation. Partially predated seeds are often viable, which may have implications for seedling demography. Seed predation and flowering phenology are not defmitively linked, strengthening the argument that flowering time is not adaptive in this species.