abstract: This is a joint work with Alex Chirvasitu and S. Paul Smith. We introduce a new method to construct 4-dimensional Artin-Schelter regular algebras as normal extensions of 3- dimensional ones. When this is applied to a 3-Calabi-Yau algebra, we obtain 4-Calabi-Yau algebras that form a flat family over a projective space. Our method is a rich source of new 4-dimensional regular algebras. On the other hand, some of the 4-dimensional regular algebras discovered by Lu-Palmieri-Wu-Zhang arise as outputs of our construction, and our result gives a new proof of regularity for those algebras.