  We discuss some of the basic features of extremal black holes in
four-dimensional extended supergravities. Firstly, all regular solutions
display an attractor behavior for the scalar field evolution towards the black
hole horizon. Secondly, they can be obtained by solving first order flow
equations even when they are not supersymmetric, provided one identifies a
suitable superpotential W which also gives the black hole entropy at the
horizon and its ADM mass at spatial infinity. We focus on N=8 supergravity and
we review the basic role played by U-duality of the underlying supergravity in
determining the attractors, their entropies, their masses and in classifying
both regular and singular extremal black holes.
