The potential of solar thermal chemical-looping reforming for efficient and sustainable co-production of synthesis gas and hydrogen is discussed. In an endothermic partial oxidation step, methane reacts with oxygen released from a metal oxide to produce hydrogen and carbon monoxide. In an exothermic second step, steam reacts with the reduced metal oxide to produce hydrogen. This review summarizes the process and chemical thermodynamic foundations of solar chemical-looping reforming and provides a synopsis of materials studies that reflect the state of knowledge in 2017. The challenges and opportunities for future research and development are discussed. (C) 2017 Elsevier Ltd. All rights reserved.