Abstract
Classification of smectic liquid crystal mesophases has been based on the concept of comiscibility between like phases. Based on thermodynamic principles this categorization scheme is not related directly to the structures of the phases. The elucidation of the structures of the various smectic modifications has shown that each miscibility group possesses a set of structural parameters common to all examples of that group. Also present are structural factors which form subsets of the miscibility group. These two sets of structural characteristics are defined for each miscibility group.