  We study four-dimensional N=1 gauge theories arising on D3-branes probing
toric singularities. Toric dualities and flows between theories corresponding
to different singularities are analyzed by encoding the geometric information
into (p,q) webs. A new method for identifying global symmetries of the
four-dimensional theories using the brane webs is developed. Five-dimensional
theories are associated to the theories on the D3-branes by using (p,q) webs.
This leads to a novel interpretation of Seiberg duality, as crossing curves of
marginal stability in five dimensions.
