  The notion of generalized Bell numbers has appeared in several works but
there is no systematic treatise on this topic. In this paper we fill this gap.
We discuss the most important combinatorial, algebraic and analytic properties
of these numbers which generalize the similar properties of the Bell numbers.
Most of these results seem to be new. It turns out that in a paper of Whitehead
these numbers appeared in a very different context. In addition, we introduce
the so-called $r$-Bell polynomials.
