Organic template-directed mineralization of calcite crystals has been probed in situ by external reflection-absorption FTIR spectroscopy in an effort to understand the dynamics of the organic-inorganic interface during crystal growth. The main focus is to elucidate structural changes that may occur in the organic template as crystal growth progresses. The nucleation face types of calcite were visually identified according to known crystal morphologies and by the corresponding carbonate stretching and deformation vibrational bands. Structural reorganization occurring in the organic template could be observed by intensity variations and frequency shifts in the methylene stretching bands of octadecanoic acid, octadecyl sulfate, and acidic polydiacetylenic lipid film, These organic templates nucleated calcite at the (010), (001), and (012) planes, respectively. The surfactant thin films uniquely adapt themselves in order to optimize the geometrical and stereochemical fit to the growing calcite crystals.