The problem of the physical mechanisms of collective magnetic behavior, both static and dynamic, of an assembly of ferromagnetic particles comprising a nanocomposite material has been addressed. Detailed measurements of magnetization curves and microwave absorption spectra of films prepared from chemically synthesized (polyol technique) Fe–Ni–Co particles of various shapes and sizes have been performed. It has been shown that the dipole-dipole interparticle interactions play an important role in the magnetic behavior of such systems. An original method, relying on the shift of the magnetization curves in parallel and perpendicular geometry due to the planar anisotropy, allowing estimation of the concentration of magnetic particles has been proposed. The measurements of microwave absorption spectra at 9.5 GHz have revealed the features typical of local resonances localized on individual nanoparticles (Kittel mode and the lowest SWR) as well as those that can be attributed to collective behavior due to dipole-dipole interactions. It has been demonstrated that magnetization reversal is accompanied by a microwave hysteresis.