The word “dominance,” in the context of genetics, has been used for a long time applied to characters or to alleles. A dominant character masks the expression of an alternative form. This loose definition would even apply when these alternatives are not determined by alleles of the same locus. In turn, a dominant allele refers to an alternative version at the same locus. This dual usage has led, as expected, to some confusion and shows how statistics can complement verbal definitions. Mendel, the pioneer of genetics, did not know the bases of the phenomenon of dominance. Nor was he completely certain to look at characters defined by alleles. But the ubiquity of the phenomenon caused him to elevate his observations to the category of laws, that went, unfortunately, unnoticed until they were rediscovered decades later. Today, dominance and recessivity are concepts commonly used and not only by geneticists. Yet a question remains: do we really understand the mechanisms of dominance? The Biology of Genetic Dominance seeks to answer this question through observation and insight. Its main driving force has been the enthusiasm of an international assembly of scholars who have agreed to write down their thoughts so as to enlighten our comprehension of dominance. The ambition of this collection of essays is to help in the understanding of the bases of mendelian dominance as a pre-requisite to better understand the more complex non-mendelian inheritance. This book relies upon self-contained chapters. They can be considered, in the context of the whole, as separate documents.