The Probability of Causation (PC) was introduced to compensate objectively and more possible legally the U.S. diseased subjects involved in the nuclear armament activities. The methodology is related to the attributable risk concept, but it is widely different from it, since it doesn't evaluate the "attributablity" from a collective point of view, but from a "personalistic" point, that is from the particular exposure condition, from the specific physical parameters and from the biological individual features of the single exposed subject. So the PC become an evaluation of the harm probability "tailored" for "that" specific exposed person, on the basis of the epidemiological indications coming from an exposed group with very similar characteristics of the under investigation individual. This is clearly possible owing to the large and exhaustive amount of epidemiological studies in the specific field of radiation exposure. The process to reach the PC adoption took a long time, was plodding and politically thwarted and various reexaminations and bills during time were necessary to extended the laws to the different exposure categories. Now in the U.S. three departments (Health, Energy and Labour) are involved in the evaluation processes; they gather the personal, dosimetric and clinical data and with a computer program (usable on line also) based on the updated knowledge, evaluate the eligibility for compensation on the basis of the "more likely than not" criterion. The method meets the interest and the favor at international level and organizations in prominent positions in the pacific use of nuclear energy and in the radiation protection fields, like: NCRP, IAEA, WHO, ILO,... fight for it use. Now many institutional organism and the more enlightened justice courts utilize the PC to settle cases (increasing in frequency) in work and health activities, for which more often compensation claims are dealing with.