There has been a renewed commercial and technical interest in pumped hydro energy storage (PHES) recently with the advent of increased variable renewable energy generation and the development of liberalized electricity markets. During the next 8 years over 7 GW of PHES capacity will be added to the European network while projects are also planned in the USA and Japan. This paper provides a review of existing and proposed PHES plant and discusses the technical and economic drivers for these developments. Current trends for new PHES development generally show that developers operating in liberalized markets are tending to repower, enhance projects or build `pump-back' PHES rather than traditional `pure pumped storage'. Capital costs per kW for proposed PHES in the review region range between (sic)470/kW and (sic)2170/kW, however these costs are highly site and project specific. An emergence has also been observed in recent PHES developments of the use of variable speed technology. This technology, while incurring slightly higher capital costs, offers a greater range of operational flexibility and efficiency over conventional PHES. This paper has primarily been prompted by a lack of detailed information on PHES facilities worldwide and reviews current developments in the context of market and generation mix changes. The most recent large scale review of PHES faculties was undertaken by the American Society of Civil Engineers Hydro Power Task Committee on Pumped Storage in 1996. In the absence of data in the literature on new PHES plant development, this review draws primarily on publicly available information from utilities, government bodies and electricity regulators. In the same context this study is limited to a review region of the European Union, Japan and the United States as information on developments outside these areas is difficult to procure. This paper also gives a review of locations and proposed timelines for new PHES development and provides a thorough up-to-date overview of the development trends of this technology. (C) 2009 Elsevier Ltd. All rights reserved.