A central problem in nanotechnology is the understanding of structure-to-properties relationship. This is essential for tailoring the functionalities, efficiency, and performance of the near-future materials. Here, hyperfine interactions can be employed as they instantly reflect the state of structural arrangement. Examination of the corresponding hyperfine parameters during nanocrystallization through the use of the so-called nuclear forward scattering (NFS) of synchrotron radiation is now possible. One can follow separately structural evolution of different sites of the 57Fe probe atoms. Structural transformations in metallic glasses including nanocrystallization were investigated by NFS to fine details that are completely hidden when conventional analytical tools are employed. Systematic analyses of NFS time-domain patterns provided an opportunity to study independently the role of structurally different regions. The latter comprise amorphous residual matrix, newly formed nanocrystallites, and interface regions. Different amounts of iron atoms located at the nanograins’ surfaces and in their core were observed for different crystallization conditions, viz. temperature, time, and/or magnetic field. The application of in situ NFS experiments has a huge potential for observations of the evolution of phase transformations in real time performed on fly during short time intervals.