Already Lorenz Oken and J. W. von Goethe described the vertebrate haed as a segmented structure. Ever since, the “head problem“ (Das Kopfproblem) has been a mainstay of morphological investigations and speculation. Today the question of vertebrate head segmentation is treated mostly from developmental perspectives within evolutionary developmental biology. Whether the different segmented structures (rhombomeres, branchiomeres etc.) all are coordinated and whether the head mesoderm is at all segmented remain controversial topics. Does generative constraints occur, and how do innovations arise in this complicated structure? There are, however, several other aspects to the head problem, and an integration of the new data from developmental studies at the cellular and molecular levels with e.g. the paleozoological segmentalist tradition seems necessary. The suggested project is an attempt to start this integrative work, using the analytical concepts from research into “burden“, constraints, and evolutionary innovations as guiding principles, to which reserchers at or associated with the KLI have made important contributions. Specifically, I want to contrast the idealistically oriented, but thoroughly empirical, work of the Stockholm palaeozoologists with the contemporary approach in evolutionary developmental biology, which makes comparisons basic on cladistic principles and developmental data at morphological as well as molecular levels. Methods include interviews with leading researchers familiar with the contrasts between structural and functional approaches (e.g., Gerd Müller), or who have a thorough training in the paleozoology of the Stockholm school and in cladistics (such as Philippe Janvier), as well as literature studies. The goal is to write a review paper and develop new ideas into a form mature enough to direct my experimental work.