The efforts on energy system decarbonization and improved sustainable energy efficiency in developed countries led energy enthusiasts to explore alternative highly effective pathways in accomplishing these goals. Specifically, the transition from hydrocarbon to H-2 economy using fuel cells and H-2 technologies is a sustainable and favorable approach forward in meeting stationary, transportation, industrial, residential, and commercial sectors. This review in three Parts brings out the capability of H-2 for enabling an energy revolution through much-needed flexibility in renewable energy resources. The review identifies the developments and challenges within the H-2 generation, storage, transportation, distribution, and usage - as well as applications along with national and international initiatives in the field, all of which suggest a pathway for a greener H-2 society. The review also highlights the opportunities and challenges in major energy sectors for H-2 technologies. Part I of the series highlights the importance of H-2 economy and initiatives from various agencies, and presents several H-2 generation methods. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.