We present ab initio studies of structures, energetics, and diffusion properties of Mg in bulk Si, Ge, and Sn diamond structures to evaluate their potential as insertion type anode materials for Mg batteries. We show that Si could provide the highest specific capacity (3817 mAh g−1) and the lowest average insertion voltage (∼0.15 eV vs. Mg) for Mg storage. Nevertheless, due to its significant percent lattice expansion (∼216%) and slow Mg diffusion, Sn and Ge are more attractive; both anodes have lower lattice expansions (∼120% and ∼178%, respectively) and diffusion barriers (∼0.50 and ∼0.70 eV, respectively, for single-Mg diffusion) than Si. We show that Mg–Mg interactions at different stages of charging can decrease significantly the diffusion barrier compared to the single atom diffusion, by up to 0.55 eV.