Advanced operando spectroscopic techniques monitor real-time changes in crystal structure, oxidation state, coordination environments, and chemical evolution of Na-ion host anodes during charge-discharge cycles. Operando spectroscopy techniques include Raman spectroscopy, nuclear magnetic resonance, powder X-ray diffraction, X-ray adsorption fine structure, X-ray absorption near edge and extended X-ray absorption fine structure, which provide outstanding scientific understanding of anodes for the next generation of Na-ion batteries. This review systematically summarizes intercalation, alloying, and conversion anodes investigated through operando spectroscopy techniques. These have generated a profound and fundamental understanding of diverse phenomena occurring on the active material surface and/or bulk during the electrochemical reaction conditions, such as phase transitions, side reactions, lattice parameter changes, and molecular scale structure-reactivity relationships. (C) 2019 Elsevier Ltd. All rights reserved.