The production of hydrogen from water using concentrated sunlight to drive the water-splitting process is an attractive renewable energy opportunity. Solar-thermal processing to produce electricity is practiced commercially in Spain today. It is two to three times more efficient and much lower cost than generating electricity from a photovoltaic array. Thermochemical cycles to split water require higher solar intensities and the use of materials that are chemically compatible with process reactants and products at high temperatures. Materials must also be relatively insensitive to thermal shock. Other challenges include the requirement to concentrate acids or bases from dilute acid/water or acid/base systems. Of course, processes must be compatible with the diurnal nature of sunlight and must be fairly simple with process intermediates that are easy to store. This presentation will focus on metal oxide dissociation thermochemical cycles. Experimental (both on and off sun) and theoretical results will be summarized and the challenges associated with the process development will be reviewed.