The anode candidates for Li/Na ion batteries are primarily the elements located in main groups four (IV_A) and five (V_A) in the periodic table, including C, Si, Ge, Sn, P, Sb, and their oxides or alloys. The electrochemical (de)lithiation or (de)sodiation processes of these materials usually involve (de)intercalation and/or alloying reaction of ions with lithium or sodium, and the formation of amorphous or nonstoichiometric compounds, which are beyond the detection range of diffraction patterns. In this chapter, we highlight the application and the importance of solid-state NMR (SSNMR) spectroscopy in the studies of anode materials. Ex situ and in situ ^6,7Li and ²³Na NMR studies of the most widely adopted carbon-based materials (graphite, hard carbon etc.) are introduced in the first section, followed by silicon-based (Si, SiO_x) and other alloy-type anode materials in the second section. The fundamental electrochemical processes, reaction mechanisms, and Li⁺/Na⁺ transport dynamics are all analyzed in detail based on SSNMR studies, especially under in situ conditions.