Legal responsibility comes in different forms. Private law deals with questions of responsibility for harm that someone causes another. The responsibility requires three things: That someone was harmed, that another person falls under a norm that founds responsibility under the circumstances at hand and that the reason the victim suffered harm was the behavior of that person. The basic requirements for responsibility lead to problems in some situations. Many courts around the world have struggled with cases in which the plaintiff have been exposed to a risk by the defendant where it is not possible to prove that the risk has caused a harm. For example, the risk may be of such a kind so that a harm will not appear until a time period has passed. This has produced different creative solutions in many jurisdictions. Some countries have introduced a new concept of damage, "loss of chance" or "perte d'une chance", which rests on a probability assessment of the risk of future harm. My research project will address these problems from a Swedish perspective and assess whether there is a need for adjusting the basic apparatus of private law responsibility to make room for assessments of risks/chances/probabilities.