There is an almost twelve order of magnitude difference in the seed weight of recent plant species. Studying the causes, patterns and consequences of this high variability is a crucial issue in plant ecology. In this paper we summarise the main conclusions of the studies in this topic to get a broad and general view of the possible explanations of high variability in seed weights and its consequences on dispersal, seed predation, seed bank formation, germination, establishment and plant growth, and on the structure and function of plant communities. Because of the extremely high number of papers published in this topic, we aimed at to concentrate on papers published in highranked international journals in the last few decades, having a special focus on publications from the Carpathian Basin. It was found that growth form, body size, genom size, latitude and light availability are responsible for the detected high variability in the seed weights of species. Infra-individual variability is mostly caused by the effects of the position on the maternal plant and the seed size – seed number trade-off. The effect of dispersal by wind or by seed predators on the variability of seed weights and its ecological consequences are the most studied. Predicting persistence on the basis of seed size and seed shape also has been a popular research topic lately. Studying the effects of seed weight variability on the structure of plant communities is also becoming more and more important, but no general conclusions could be drawn yet.