The Drosophila wing is divided into anterior and posterior compartments, the latter characterized by the expression of the engrailed gene. A comparative analysis is presented here, and suggests that a primary conserved role of engrailed is to drive growth of limbs along the proximo-distal axis. The Apical Ectodermal Ridge in vertebrate limbs resembles the Antero/ Posterior compartment boundary in fly wings, particularly in molecular aspects. Multiple evidence suggests that the fly wing Antero/Posterior boundary is not the result of differential cell affinities between all anterior and posterior cells, but responds to the area of cell communication between anterior and posterior compartments. Arguments are presented here to support the notion that the compartment boundary is a consequence of decapentaplegic function in the control of growth. Patterning, on the other hand, requires the participation of several genes, among which are engrailed, invected and hedgehog. Finally, regulatory interactions between en/En-1 and hh/Shh may be significant in the context of morphogenetic regulation during normal development.