A review is given of the problems in this field, and of the possibilities opened up by the fact that neutron scattering gives access to the time‐dependent spin‐correlation function in magnets over virtually the whole range ofq, t, andT. New experimental results are given in connection with magnon energy linewidth and renormalization, and some data are presented for the spin‐wave stiffness of bcc 3dtransition‐metal alloys as a function of electron concentration, showing effects explained by the electronic density‐of‐states curve. It is pointed out that the ground‐state fluctuations of magnets give rise to effects in the formulas for neutron scattering.