espanolA pesar de ser un fenomeno mundial que puede tener importantes consecuencias ecologicas, economicas y sociales, la salinizacion de los ecosistemas acuaticos (es decir, el aumento de las concentraciones de iones en sus aguas) ha sido poco estudiada en comparacion con otros problemas ambientales. Sin embargo, esta recibiendo una atencion cada vez mayor, con importantes avances cientificos realizados durante las ultimas dos decadas. Aqui reviso el conocimiento actual sobre el tema y propongo futuras direcciones de investigacion en el contexto del bienestar humano y el cambio global. La salinizacion de los ecosistemas acuaticos es causada por una amplia gama de actividades humanas, siendo la agricultura y la extraccion de recursos las mas ampliamente documentadas. Diferentes estudios sugieren que podria estar afectando alrededor de 1/3 de los cuerpos de agua dulce, y este numero probablemente aumentara en el futuro debido a los cambios en el clima y los usos del suelo. Se sabe que el aumento en la salinidad de las aguas dulces causa efectos adversos en la condicion fisica y la supervivencia de muchos organismos acuaticos, sin embargo, los mecanismos osmorreguladores que subyacen a estos efectos aun no se conocen bien. Ademas, se ha demostrado que diferentes iones pueden tener diferentes toxicidades para los organismos acuaticos, pero la mayoria de las investigaciones se han centrado exclusivamente en los iones Na+ y Cl-. Por lo tanto, se necesitan mas investigaciones sobre los efectos potenciales de .... EnglishIn spite of being a worldwide phenomenon that can have important ecological, economic and social consequences, freshwater salinization (i.e. the increase in ion concentrations in freshwaters) has been poorly studied when compared with other environmental issues. However, it is receiving increasing attention, with significant scientific advances being made during the last two decades. Here I review the current knowledge on the topic and propose future research directions within the context of human welfare and global change. Freshwater salinization is caused by a wide range of human activities, with agriculture and resource extraction being the most widely documented. Different studies suggest that it could be affecting around 1/3 of freshwater bodies, and this number will very likely increase in the future due to climate and land use changes. The increase in the salinity of freshwaters is known to cause adverse effects on the fitness and survival of many aquatic organisms, however the osmoregulatory mechanisms underlying these effects are still poorly understood. Moreover, it has been proved that different ions can have different toxicities to aquatic organisms, but most of the research has focused exclusively on Na+ and Cl-. Thus, more investigations on the potential effects of increasing concentrations of other specific ions (e.g. K+, SO42-) are needed. The impact of salinization on freshwater biodiversity can alter ecosystem functioning, although only a few functions have been studied (e.g. leaf litter decomposition). Also, freshwater salinization can affect the delivery of ecosystem services and have direct economic (e.g. infrastructure corrosion) and social (e.g. human health) impacts that have rarely been assessed. The management of this urgent environmental issue needs to be improved through mitigation (e.g. backfilling of mine tailings), remediation (e.g. enhanced wastewater treatment), prevention (e.g. using alternative deicers for roads) and monitoring (e.g. estimating salt loads to freshwater ecosystems) actions.