The cell biological perspective on the evolution of the Fetal-Maternal Interface has several historical roots. The best known is the immunological paradox, i. e. the maternal tolerance of a semi-allogenous tissue in her body. Clinicians complain this view misleads clinical practice by pushing an incomplete paradigm based on a flawed analogy between an embryo and a xenotransplant. In this book the authors explore three alternative views of this interface: the cell biological paradox involved in embryo attachment, the inflammation paradox, and the tissue biological paradox. The conceptual core of this book is derived from the biological details of these paradoxical metaphors. The unifying idea is that evolutionary transformation of parts of the organism are opposed by the homeostatic tendencies of the body itself. Chapters explore innovations realized by mechanisms overcoming or modifying existing homeostatic mechanisms. On the other hand, the homeostatic mechanisms themselves can become the seed for evolutionary change, such as cellular stress mechanisms. A collateral topic is dedicated to a methodological critique of a popular research approach in evolutionary reproductive biology – the comparative method. Our critique is less directed towards the technical implementation of the comparative method, which is largely fine, but the anterior problem of how to represent the data and how to define the research questions. Another equally fascinating topic covered is the hypothesized connection between the evolution of invasive placentation and the evolution of cancer malignancy.