This article describes Natural Computing, an interdisciplinary research field in which nature is the inspiration source of new Computer Science methodologies. Natural Computing includes a wide spectrum of different themes, that differ each other on aims and means. For instance, there is a theme in which the theory of evolution by natural selection inspires methodologies for solving problems of computational mathematics. Another example is a theme in which DNA molecules are used to execute very complex algorithms with performances that cannot be obtained by current electronic computers. Moreover, there are several themes in which mathematical and computational models are used to understand the mechanisms underlying the functioning of cells. The themes of Natural Computing can be grouped in two main categories: (i) new computational models and methodologies inspired by natural phenomena, and (ii) applications of computational models and methodologies to the study of natural phenomena. The aim of the themes of the first category is to contribute to the research in Computer Science by using nature as an inspiration, whereas the aim of the themes of the second category is to contribute to the research in Life Sciences by using computational means. The objective of this article is not to survey all of the Natural Computing themes, but to describe what could be concretely obtained in this research field by focusing on two representative themes: "Evolutionary Computation" and "DNA Computing".