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Germanium is a promising active material for high energy density anodes in Li-ion batteries thanks to its good Li-ion conduction and mechanical properties. However, a deep understanding of the (de)lithiation mechanism of Ge requires advanced characterizations to correlate structural and chemical evolution during charge and discharge. Here we report a combined operandoX-ray diffraction (XRD) and ex situ7Li solid-state NMR investigation performed on crystalline germanium nanoparticles (c-Ge Nps) based anodes during partial and complete cycling at C/10 versusLi metal. High-resolution XRD data, acquired along three successive partial cycles, revealed the formation process of crystalline core–amorphous shell particles and their associated strain behavior, demonstrating the reversibility of the c-Ge lattice strain, unlike what is observed in the crystalline silicon nanoparticles. Moreover, the crystalline and amorphous lithiated phases formed during a complete lithiation cycle are identified. Amorphous Li7Ge3and Li7Ge2are formed successively, followed by the appearance of crystalline Li15Ge4(c-Li15Ge4) at the end of lithiation. These results highlight the enhanced mechanical properties of germanium compared to silicon, which can mitigate pulverization and increase structural stability, in the perspective for developing high-performance anodes.