The aim of this paper is to dissect the hierarchical structures of BaTiO3 particles into primary, secondary, tertiary, and quaternary structural levels and to thoroughly review the corresponding structureferroelectricity relationships at all levels. This analytical framework is of growing importance for the fundamental understanding of the ferroelectric properties of BaTiO3 in microelectronic devices, especially as their structural levels are all approaching the same scale in the process of miniaturization. The identification of the most influential structure among others and the deduction of a meaningful structure-ferroelectricity relationship depend on a thorough understanding of the relationships.