This book introduces a new evolutionary model called Hierarchical Evolutionary-Developmental Theory or H-Evo-Devo Theory. This theory proposes that the organism’s internal properties reflect entities that are highly integrated in developmental terms that evolve hierarchically. In particular, it emphasizes the importance of “developmental constraints.” These constraints operate at different scales, producing distinct states of morphological stability reflected as subspecies, species, higher taxa, and homologues, all representing units of evolution. Microevolution is the subspecies level. Macroevolution is the species level. Megaevolution is the higher taxa level. Modular-evolution is the homologue level. Each of these levels exhibits patterns of origin, stability, and extinction. Thus, the study of evolution aims to explain the mechanisms involved in these patterns, and the H-Evo-Devo Theory tackles these challenges. In short, the H-Evo-Devo Theory establishes a new synthesis between systematics, morphology, and evolution, suggesting a reinterpretation of the taxonomic structure and the evolutionary processes overall. Importantly, this model significantly diverges from the achievements reached by the Modern Synthesis, and it attempts to explain the phenomenon of evolution from a completely different angle.