This book aims to cover both the ontological determination and the characterization of what we call with terms such as disease and others related. The current edition is a more complete version of the first edition in Spanish that was published four years ago. In this edition, both semantic and gnoseological as well as ontological issues have been developed in more detail and depth. The foregoing is due to the fact that we could establish the meaning of the disease concept based on its explicit ontological reference, namely, the question about the existence of disease. Furthermore, to achieve that aim, it is appropriate to consider the essential properties of live systems. Consequently, this edition has reviewed in greater depth what is related to bioplasticity and macromolecular interactive processes of live systems, including epigenetic processes.