The development of the gastrointestinal tract, like that of other organs, results from the association of intrinsic genetic endowment, endogenous regulatory mechanisms and environmental influences. The present chapter emphasizes the role of epithelial-mesenchymal interactions during development and crypt-villus migration. Arguments are given as to the role of basement membrane molecules as mediators for these cell interactions. Differential developmental expression of the various extracellular matrix components, which precedes the onset of differentiation markers, suggests that each of these molecules assumes a specific task. Yet, much work still remains to be done before knowing exactly how transfer of morphogenetic signals between epithelial and mesenchymal tissues occurs.