The Energy Storage TCP hereby presents the annual report 2017. The international focus on accelerating the energy transition from fossil fuels to a renewables-based energy system increases the need for more flexibility. This is needed to match the variable production of renewable energies (like wind and solar) with variable and changing demand profiles. This requires flexibility between time of use and production as well as interaction between sectors (sector coupling). In each case energy storage in any form is required to provide affordable solutions. Whether that be storage solutions at a large scale (such as pumped hydro storage or the conversion of surplus electricity into hydrogen) or more decentralised thermal or electrical energy storage solutions in the build environment, industry and mobility sector; all will be needed. With a growing interest in energy storage technology and an identified need to deploy more energy storage, a better assessment of the “value” of energy storage, like the “value” of flexibility is required. The ambition of ECES TCP is to contribute to this development by coordinating and stimulating the international collaboration on research and development toward new and innovative energy storage concepts. The Annual Report 2017 gives an overview of the activities the Energy Storage TCP and the annexen.