Groundwater dependent ecosystems (GDEs) are ecosystems in which environmental conditions rely on a consistent supply of groundwater. Over the past two decades, they have been increasingly studied worldwide. However, GDEs located in regions sufficiently far north to experience freezing winter temperatures and precipitation that exceeds evapotranspiration have generally received limited scientific attention. Nevertheless, these ecosystems, which are of considerable ecological value, are subject to growing human pressures. GDEs are particularly vulnerable to disruptions in their ecohydrological functions caused by human activities such as groundwater extraction, drainage, and land-use change, all of which alter groundwater levels and the way aquifers sustain these ecosystems. Long-term shifts in temperature and precipitation patterns driven by climate change also pose potential threats to GDEs. Understanding present-day GDEs and preventing further degradation is essential for their conservation. The objective of this book is to describe interactions between GDEs and groundwater from a hydrogeological perspective. The focus is on GDEs typically located in mid- to high-latitude regions of the Northern hemisphere and below the permafrost limit. Target regions are characterized by cold, humid climates with snowy winters and relatively warm summers, where annual precipitation substantially exceeds evapotranspiration. The book first addresses GDE types, geomorphological settings, hydrology, and geochemistry in separate chapters, followed by an examination of the impacts of human activities and climate change on these ecosystems. Case studies and thematic insights are presented in dedicated boxes within each chapter, along with applied examples illustrating the use of hydrogeological and hydrogeochemical methods for monitoring and characterizing GDEs.