The way our decisions and actions can affect future generations is surrounded by uncertainty. This is evident in current discussions of environmental risks related to global climate change, biotechnology and the use and storage of nuclear energy. The aim of this paper is to consider more closely how uncertainty affects our moral responsibility to future generations, and to what extent moral agents can be held responsible for activities that inflict risks on future people. It is argued that our moral responsibility (...) to posterity is limited because our ability to foresee how present decisions and activities will affect future people is limited. The reason for this is primarily that we are in a situation of ignorance regarding the pace and direction of future scientific and technological development. This ignorance reduces our responsibility in a temporal dimension because in most areas it is impossible to predict the interests and resource needs of future generations. In one area, however, we have fairly reliable knowledge about future people. It is reasonable to assume that future human beings will have the same basic physiological (physical and biological) needs as we have. On this basis, it is argued that we can be held responsible for activities causing avoidable damage to critical resources that are necessary to provide for future physiological needs. Furthermore, it is suggested that it is prima facie immoral to impose risks upon future generations in cases where the following conditions are fulfilled: (1) the risk poses a threat to the ability of future generations to meet their physiological needs, and (2) the risk assessment is supported by scientifically based harm scenarios. (shrink)