The once deeply engrained idea that water management should be considered as a technical endeavour that is appropriately confined to hydrological science and hydraulic engineering has now largely ceded to the recognition that water issues also comprise important social and political dimensions that call for the involvement of social science and multiple stakeholders. As such, in recent years, increased attention has been paid to the nature and effects of water policies, the roles of different water users in decision-making , and the emergence of conflicts and cooperation around water at various scales. These social and political dimensions of water have been subject to significant theoretical advances, drawing especially on insights from the broadly-defined political ecology tradition (including elements of science studies and anthropology), that seek to transcend Cartesian dualisms between humans and the environment in favour of the co-constitution between society and nature. Unlike conventional studies that focus on the relationship between humans and water conceived of as two distinct categories that interact with one another, considering water as socioecological makes it impossible to abstract water from the social context that gives it meaning and from the socio-political processes that shape its material flows and its discursive representations. In line with this perspective, the notion of a hydrosocial, as opposed to a hydrological, cycle has gained traction as a means of both capturing and integrating the socio-political and biophysical processes that constitute water, as well as highlighting the limitations of traditional science and practice. The hydrosocial cycle is purposefully contrasted with the hydrological cycle, which is a dominant and enduring concept for portraying the physical states and flows of water, yet arguably regards water and water processes as asocial and apolitical. However, as the use of the term (alongside and beyond other uses of the term 'hydro-social' or 'hydrosocial') has proliferated, different meanings and usages have become apparent that suggest the need for further scrutiny. The concept of the hydrosocial cycle has hitherto been deployed to capture the deepening entanglement of water flows and power relations, and to shed light on the politicised nature of water management, with a view to reinterpreting the social and ecological implications that emerge as effects of power relations rather than of policy styles (Bakker, 2003a, 2003b; Swyngedouw, 2006, 2009). To date, the flows of water and social power embedded within the hydroso-cial cycle have been examined in a range of contexts and from different perspectives, including through the capitalist production of urban environments (Kaika, 2005; Swyngedouw, 2004), the historical construction and mobilisation of the concept of the hydrological cycle (Linton, 2008, 2010), and the production of hydrological assessments that reinforce unequal access to water (Budds, 2008, 2009) (see Linton and Budds, 2014, for a comprehensive review of previous scholarship employing the term 'hydrosocial cycle'). This special issue on the hydrosocial cycle responds to the need to more precisely define and theorise the concept as a means to interrogate and elucidate hydrosocial relations and change, as well as to explore and articulate its analytical and political purchase for critical water research and action. The endeavour commenced through a shared interest among the organisers in the politics of hydrology, and an aspiration to integrate this aspect more fully into the growing and vibrant body of work around political ecolo-gies of water, little of which had hitherto paid much attention to the construction and implementation of hydrological concepts, methods and data. We pursued this interest through a series of panel and paper sessions at the Association of American Geographers annual meetings in 2008 (Water, Science, Humans: Adventures of the Hydrosocial Cycle), 2009 (Water, Science, Humans: Advancing the Hydrosocial Cycle) and 2010 (The Hydrosocial Cycle: Between Hydrology and Critical Social Science), which attracted wide interest and participation from human geographers and cognate scholars. Through our engagement in these sessions, our initial aim to reflect on the nature and place of hydrology in political ecologies of water developed into a much broader endeavour to further understandings of the relationships between water, people and science, with a view to refine the nature of the concept of the hydrosocial cycle and contemplate the ways in which it might support and advance critical political ecologies of water within academic scholarship, that may in turn inform water policy and practice, as well as feed new perspectives into interdisciplin-ary water education. The primary aim of the collection of papers assembled in this special issue is thus to further consolidate the concept as a framework that focuses attention on the materiality of water flows in conjunction with the social and political practices and discourses that shape and are shaped by them. This need is justified by observations that hydrological processes are increasingly influenced by human activities and institutions with specific visions and motives, that hydrological data and knowledge are acknowledged as socially constructed and politically mobilised, that water is increasingly recognised as being characterised by multiple and context-specific cultural meanings, and that the material and symbolic characteristics of water also play an important role in shaping social relations and forms of governance. A core contention of this collection of papers, therefore, is that, while the hydrological cycle remains a widely used framework for understanding biophysical processes, it is lacking for the analysis of water governance, politics and conflict.