This book proposes the foundation of the relational approach to biology, rejecting the deterministic and reductionist approach of molecular biology. Although biology has made enormous progress in the last seventy years, onto genesis is still conceived as a “revelation” of information (DNA). Recovering the geometric tradition, relational biology conceives scientific and epistemological tools (cause, probability, space etc.) of science in a new way. If probabilistic biology and organicism still proposes a biology based on physics, with a fundamental invariant, relational biology is based on variation: its fundamental invariant is variation, one of the most important elements of life. This is an indispensable book for academics who consider biology from a new theoretical approach, in particular for those working in the domains of cancer, ontogenesis and evolution.