In spite of the fact that few dietary components are so widely recognized as able to improve human health such as ?-3 polyunsaturated fatty acids (PUFAs), so that their sector in the nutritional market has been increasingly growing worldwide, many unresolved questions still remain about them. In particular, there is urgent need for better understanding their possible role as anti-neoplastic agents. First of all, the chemical structure, the intracellular metabolism, and the dietary sources and bioavailability of these dietary fatty acids will be described in this introductive chapter to make easier the comprehension of the remaining parts of the book.