Hydrogen as an energy vector is seen as a fundamental enabler to the energy transition toward a low-carbon energy future not only from the power perspective but also from a primary energy one. In fact, not only is it conceivable as an electricity storage method (Power-to-X-to-Power) that can contribute to the safe increase of penetration stochastic renewable electricity to the grid but it also represents a versatile cross-vector medium enabling the deep decarbonization of non-electrified hard-to-abate sectors (renewable fuels, sector integration, mobility, etc.). In this context, great political and economic interest has risen related to the deployment of hydrogen technologies in the past few years, leading most key players – both industries and institutions – to include hydrogen technologies in national industrial strategies and development programs. In this chapter – after a brief overview of the state of the art of the main hydrogen technologies (declined for each section of the value chain) – an application-driven analysis of what will be the foreseen role of hydrogen technologies in future integrated energy systems is provided, considering a wide range of applications such as energy storage, grid flexibility services, renewable feedstocks for heavy industries, and fuel cells for both stationary μ-CHP and automotive applications. Ultimately, a list of worldwide key breakthrough projects of the period 2000–2020 is provided to show the history and development of hydrogen technology toward market maturity.