 The relationships that obtain between development and evolution are complicated and under ongoing investigation (for a review, see Love 2015). Two main axes dominate within a loose conglomeration of research programs (Raff 2000; Müller 2007): (a) the evolution of development, or inquiry into the pattern and processes of how ontogeny varies and changes over time; and, (b) the developmental basis of evolution, or inquiry into the causal impact of ontogenetic processes on evolutionary trajectories—both in terms of constraint and facilitation. Two examples where the concepts and practices of developmental and evolutionary biology intersect are treated here: the problematic appeal to functional homology in developmental genetics that is meant to underwrite evolutionary generalizations about ontogeny  (Section 5.1)  and the tension between using normal stages for developmental investigation and determining the evolutionary significance of phenotypic plasticity  (Section 5.2).  These cases expose some of the philosophical issues inherent in how development and evolution can be related to one another.