The paper summarizes the results of neutron scattering from a weak itinerant ferromagnet MnSi (the itinerant electron system) and Invar alloys: Fe65Ni35and Fe3Pt (the quasi‐localized spin system). Well defined spin wave excitations as well as the excitations in the Stoner continuum could be detected at 5 K for MnSi in the induced ferromagnetic state. The spin dynamics in this weak itinerant ferromagnet were found to be compatible with a simple theory of an itinerant ferromagnet within RPA. The Stoner boundary is located at about 2.5 meV and the magnetic properties of MnSi are mainly determined by the Stoner excitations. In the case of Invar alloys, spin wave excitations could be detected up to 80 meV. The itinerant character of the magnetic properties is suggested not to be due directly to the Stoner excitations but to interactions between the spin waves and the Stoner modes in some higher order mechanisms.