The prediction of future events from our knowledge of past events is one of the main functions of Science. Such predictions are made possible by inferring causal relations between events from observed regularities. These relations are then codified into “laws of nature,” and it is through knowledge of these laws that prediction becomes possible. The concept of “causal relation” is thus a fundamental one in the structure of science. Now recent advances in physics have led scientists to modify considerably their views of this concept. It has been found necessary to abandon the idea of rigidly deterministic causal relations, and substitute in its stead relations that are only determined with a certain degree of probability. The main purpose of this paper is to analyse the meaning of these changes in our concepts of causality.