The embryonic development of bicuspid aortic valve (BAV) has been mainly studied in spontaneous and genetically manipulated rodent models with a high degree of extrapolation to the human species. BAV formation relays on two alternative embryonic anatomical abnormalities, i.e., the anatomical fusion of two adjacent valve primordia, and the absence of one valve primordium. These abnormalities develop as a consequence of three morphogenetic defects occurring at three different possible valvulogenetic stages, namely, (1) during the formation of the endocardial cushions (pre-septation stage), by alterations in the cellularization of the endocardial cushions (invasion of cardiac neural crest (CNC) cells; endocardial-mesenchymal transition (EMT) process; proliferation of second heart field (SHF) derived cells, (2) during the outflow tract septation (septation stage), due to excessive fusion of the conotruncal ridges, or (3) during the excavation of the valve cushions (excavation stage), due to alterations in the proliferation, apoptosis, and/or matrix secretion of mesenchymal cells in the hinges of the valve primordia. Although defects in multiple molecular pathways may cause BAV formation, NOTCH seems to be a central pathway in BAV development through regulation of two key cellular mechanisms, namely, CNC behavior and its interaction with the secondary heart field-derived mesenchymal cells and EMT.