We thought we knew that the cells in our body are an expression of DNA, the code that defines each of us as unique and ultimately our identity. Now, however, we are discovering that this idea of ​​the "self" is misleading. For several years, scientists have been investigating microchimerism, a biological phenomenon that indicates the presence of a certain number of cells with a genetic makeup different from those of the rest of the host organism. These foreign cells communicate with our own, participate in the functioning of our organs, help repair damaged tissue, and can contribute to fighting infections. This is a discovery that transcends the purely scientific realm and proves capable of raising existential questions: the boundaries of the person are constantly being questioned and the definition of the self becomes provisional. This book tells the story of an ongoing revolution that opens the door to a dizzying variety of futures, the forms of which are only just beginning to take shape.