This book explores the unity of life. It proposes that the concept of information is the inner essence of what we today call life. The importance of information for our species is obvious. Human beings are highly dependent on information, constantly exchanging with conspecifics. In a less apparent way, we are the product of genetic and epigenetic information which determines our development in a given environment from a fertilized egg to the adult stage. Even less apparent is that information plays a determining role in ecosystems. This observation may include the prebiotic systems in which life emerged. Our claim is that Nature processes information continuously. This means that even beyond living entities, we can see messages and decoding procedures. Nature can be said to send messages to its own future and then to decode them. Nature "talks" to itself! The systematic organization of messages suggests that, in some respects, we should even speak of the "languages" of Nature.