The magnetic susceptibility of a spin glass (e. g. Cu with 1-10 % Mn) has a sharp cusp at the local ordering temperature, rapidly rounded off by an external magnetic field. We show how the local molecular field theories can be generalized to account for this effect. One defines a local order parameter which is a collective featue of the whole solid due to the random position of the spins and their long-range, oscillatory interaction (RKKY). The critical temperature for the disappearance of local order is therefore unique, as, for example, the screening length of a perturbation in a metal is a unique, collective contribution of all the electrons.