  We review the idea of Hilbert Series as a tool to study the moduli space and
the BPS operators of four dimensional N=1 supersymmetric field theories. We
concentrate on the particular case of N=1 superconformal field theories living
on N D3 branes at toric Calabi-Yau singularities. The main claim is: it is
possible to write down explicit partition functions counting all the local BPS
operators for generic N number of branes, and obtain important informations
about the BPS operators, the moduli space and the dual geometry.
