When looking at future energy systems, hydrogen offers a range of benefits as a clean energy carrier, which are receiving great attention as policy priorities. This is first and foremost as an alternative fuel in the transport sector. Car makers have recently started the market introduction of fuel cell electric vehicles and are currently entering a pre-commercial phase, as they are progressing from prototype vehicles for demonstration to producing small volumes. At the same time, market development initiatives aiming at implementing hydrogen refuelling station networks are spreading in Europe, Asia, and the USA. But also in recent years, hydrogen electrolysis has gained considerable attention as a potential flexibility option to help facilitate the large-scale integration of intermittent renewable energies. Given the sustained interest in and controversial discussions on the prospects of hydrogen, this paper aims to provide a comprehensive coverage of the most relevant aspects related to the wider use of hydrogen in the energy system, including the most recent developments and insights. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.