This book consists of the articles from the special issue of “New developments in mode-water research: Dynamic and climatic effects” in the Journal of Oceanography, Vol. 68 No. 1, 2012, comprising 10 chapters that cover a wide spectrum of topics. Topics range from the formation, circulation, and variability of mode waters to their dynamic effect on surface current and climate impact, and point to new directions for mode-water research. How do mode waters vary on decadal and longer timescales, and how will they change in response to global warming? What causes mode-water variability, and how does it affect surface circulation and climate? What are the roles of mesoscale eddies in the formation and dissipation of mode waters and in their variability and change? This book serves as a signpost in our endeavor to answer these and other challenging questions.