  We get asymptotics for the volume of large balls in an arbitrary locally
compact group G with polynomial growth. This is done via a study of the
geometry of G and a generalization of P. Pansu's thesis. In particular, we show
that any such G is weakly commensurable to some simply connected solvable Lie
group S, the Lie shadow of G. We also show that large balls in G have an
asymptotic shape, i.e. after a suitable renormalization, they converge to a
limiting compact set which can be interpreted geometrically. We then discuss
the speed of convergence, treat some examples and give an application to
ergodic theory. We also answer a question of Burago about left invariant
metrics and recover some results of Stoll on the irrationality of growth series
of nilpotent groups.
