Challenges for future hydrology were reviewed from the view points of interdisciplinary and transdisciplinary studies. Interdisciplinary studies on hydrology were categorized into 1) connections between adjunct disciplines because of seamless movement of water, and 2) integrated understanding of hydrology with different discipline. Transdisciplinary studies on hydrology were discussed in terms of “Future Earth (International research platform for global sustainability)” and “Panta Rhei (International Association of Hydrological Society)” as well as the strategic research agenda on hydrology, to solve the “wicked problems” as co-design, co-production and co-delivery for the sustainable society. Challenges for future hydrology were discussed from the view points of system knowledge, target knowledge and transformation knowledge. Regarding the system knowledge, the nexus including water beyond the interaction, and water footprint with sustainability indices are keys as the center of the information and process among nature, society and humanity. Backcast scenarios and future design are important for the target knowledge. Transformation knowledges are related to human behavior changes and technological innovations. Natural and social tipping points, regime shifts and resilience are keys for the future hydrology and the sustainable society.