Abstract: Real hypersurfaces in a complex space $\mathbb C^N, N \geq 2$, satisfying the Levi non-degeneracy condition, were very well studied in the famous works of Poincare, Cartan, Tanaka, Chern and Moser and in a large number of further papers. The Levi-degenerate case, which is trivial for $N=2$ (all Levi degenerate hypersurfaces in this case are essentially flat), turns out to be absolutely non-trivial for $N=3$. The reason is that a hypersurface in $\mathbb C^3$ can have Levi form of rank $1$ at a generic point, and, in this case, is neither Levi-flat nor Levi non-degenerate. If, in addition, it satisfies some non-degeneracy condition, guaranteeing that it can not be reduced to a product of a hypersurface in $\mathbb C^2$ and a complex line, the hypersurface is called 2-nondegenerate. 2-nondegenerate hypersurfaces in $\mathbb C^3$ were deeply studied in a series of papers by Ebenfelt, Beloshapka, Zaitsev, Merker, Fels and Kaup and many other authors, but a lot of essential questions, concerned with their holomorphic classification and symmetry groups, remained opened. In the present talk we demonstrate a new approach to the study of 2-nondegenerate hypersurfaces, based on the consideration of degenerate quadratic models. This new point of view enables us to give a complete solution for most of the above open questions.