A 57Fe Mössbauer spectrometry applied in a broad range of temperatures and external magnetic fields is presented as a powerful investigating tool for the structural and magnetic characterization of maghemite (gamma-Fe2O3) nanoparticles, which presently constitute a modern advanced material used in various fields of scientific, technological, and biomedical interest. Reflections of structural and magnetic properties in the hyperfine parameters of Mössbauer spectra of nanomaghemite samples prepared by different routes with varying particle size distribution, particle morphology, and degree of interparticle interactions (isolated nanoparticles, powders, nanocomposites, films) are reviewed. Some crucial points concerning the description of the magnetic regime of strongly interacting maghemite nanoparticles are also briefly discussed with respect to their Mössbauer spectra.