  Given an ideal of forms in an algebra (polynomial ring, tensor algebra,
exterior algebra, Lie algebra, bigraded polynomial ring), we consider the
Hilbert series of the factor ring. We concentrate on the minimal Hilbert
series, which is achieved when the forms are generic. In the polynomial ring we
also consider the opposite case of maximal series. This is mainly a survey
article, but we give a lot of problems and conjectures. The only novel results
concern the maximal series in the polynomial ring.
