Groundwater in the hydrological cycle. An introduction to the largest freshwater reserve on Earth discusses the role and importance of groundwater in the hydrological cycle on planet Earth. Over the past decade, many books have been published on the growing global water crisis. Although many of these books focus on the immense importance of fresh water to humanity and the many problems related to water availability, none of them have been written by experts in hydrology that deal with the corresponding to groundwater within the hydrological cycle for a wide audience in such an integrated way as this one does. The thesis of the book is strong: underground water is indispensable to guarantee human and ecological needs. Especially when the human pressure on natural resources is very strong and the impacts are very serious. In addition, the influence of climate change will make current management models unviable and it will be necessary to think of new forms of management, based on environmental protection and social justice. The text highlights that underground water is the most unknown part of the hydrological cycle and that it is necessary to know its dynamics in order to face the challenges mentioned in the governance of this natural resource essential for life. The work is part of the Groundwater Project , a non-profit organization registered in Canada in 2019 committed to contributing to educational progress and bringing a new vision to the creation and dissemination of knowledge for understanding and problem solving related to hydrogeological resources. The GW-Project operates from the website gw-project.org , as a global platform for the democratization of knowledge in hydrogeology. Technical sheet: Eileen Poeter, Ying Fan, John Cherry, Warren Wood, Douglas Mackay, 2020 Groundwater in the hydrological cycle. An introduction to the largest freshwater reserve on Earth The Groundwater Project, Guelph, Ontario, Canada. Translator: Josep Mas-Pla ISBN: 978-1-77470-028-0