There is mounting concern over the sustainability of global energy supplies. Among the key drivers are: ( i ) global warming, ocean surface acidification and air pollution, which imply the need to control and reduce anthropogenic emissions of greenhouse gases (especially carbon dioxide), nitrogen oxides, sulfur oxides, unburnt hydrocarbons and fine particles; ( ii ) the low estimated reserves of oil and natural gas; ( iii ) the need for energysecurity adapted to each country, such as decreasing the dependence on fossil-fuel imports (in particular, the vulnerability to volatile oil prices) from regions where there is political or economic instability; ( iv ) the expected growth in world population with the ever-increasing aspiration for an improved standard-of-living for all. Hydrogen is being promoted world-wide as a total panacea for energy problems. As a versatile carrier for storing and transporting energy from any one of a myriad of sources to an electricity generator, it isargued that hydrogen will eventually replace (or at least greatly reduce) the reliance on fossil fuels and thereby also avoid/decrease emissions of carbon dioxide. Not unexstorage, conversion and end-use of this energy vector. In addition, there are many policy, regulatory, economic, financial, investment, environmental and safety questions to be addressed. Notwithstanding these obstacles, it is indeed plausible that hydrogen will become increasingly deployed and will compete with traditional systems of energy storage and supply. Future roles for electrochemical power sources batteries, supercapacitors, photoelectrochemical cells and fuel cells --on the pathway to universal energy sustainability in stationary, mobile-power and road transportation applications are examined.