The book aims to provide an overview of the currently most important practical applications of genetic engineering. The main topics are the fields of nutrition and medicine. After outlining the facts—what manipulations are used and what goals they aim to achieve—emerging or expected problems and risks are described. The area of problems and dangers is very large in agriculture. It involves biological and health aspects, as well as social issues and ethical concerns. In medicine, where genetic engineering is accepted, a closer look reveals various problems, primarily in the social, personal, and ethical domains. The originally hoped-for area, gene therapy, which was expected to bring about true miracles, is associated with dangerous side effects. Similarly, there is currently a focus on the therapeutic potential of stem cells.