This book has argued for the reality of a class of biological entities that have a hard time finding their place in a theory of evolution based on genetics and population biology. These entities, or developmental types, include cell types, homologs, and body plans. The book has also provided examples that already have empirical data to see whether such ideas are contradicted by known facts about certain well-studied organ systems, like limbs, skin appendages, and flowers. This concluding chapter summarizes the book's central claims about homology, characters and character identity, and cooperativity in gene regulatory networks. It also discusses some of the lessons derived from reviewing the literature on these paradigms of devo-evo research as well as the challenges inherent in this perspective of developmental evolution.