In this book, I introduce a new theory of evolution within a hierarchical framework called Hierarchical Evolutionary-Developmental Theory or H-Evo-Devo Theory. This chapter provides the first description of this model. By incorporating hierarchies into the Evo-Devo context, this model emphasizes the concept of developmental constraints as the primary mechanism. Developmental constraints are established from a procedural hierarchy, exemplifying the interactions within the developmental process across different levels. However, the phenotypic outcomes of this process are examined by a compositional hierarchy, allowing for the identification of evolving entities in a phylogenetic context. In this regard, developmental constraints operate hierarchically, both upward and downward, producing distinct states of morphological stability that result in different evolutionary entities. The homologue represents the highest entity in the hierarchy, and the character states of homologues within the whole organism generate a series of steady states at various scales, which can be interpreted through the Linnaean hierarchy as subspecies, species, and higher taxa. In short, developmental constraints draw a single compositional hierarchy that enables the identification of homologues, higher taxa, species, and subspecies as units of evolution.