  Many materials quenched into their ordered phase undergo ageing and there
show dynamical scaling. For any given dynamical exponent z, this can be
extended to a new form of local scale-invariance which acts as a dynamical
symmetry. The scaling functions of the two-time correlation and response
functions of ferromagnets with a non-conserved order parameter are determined.
These results are in agreement with analytical and numerical studies of various
models, especially the kinetic Glauber-Ising model in 2 and 3 dimensions.
