Starting from the working hypothesis that both physics and the corresp
onding mathematics have to be described by means of discrete concepts
on the Planck scale, one of the many problems one has to face in this
enterprise is to find the discrete protoforms of the building blocks o
f continuum physics and mathematics. A core concept is the notion of d
imension. In the following we develop such a notion for irregular stru
ctures such as (large) graphs and networks and derive a number of its
properties. Among other things we show its stability under a wide clas
s of perturbations which is important if one has 'dimensional phase tr
ansitions' in mind. Furthermore we systematically construct graphs wit
h almost arbitrary 'fractal dimension' which may be of some use in the
context of 'dimensional renormalization' or statistical mechanics on
irregular sets.