This research examines the water - energy - climate change nexus to delineate policies that harmonize the nexus favourably. Typically, the energy-climate nexus has been studied as a mitigation problem, the water-energy nexus as a resource & development issue and the water-climate nexus from the water supply dimension. This research, however studies the nexus in an integrated framework. Specifically, the research aims to answer the following questions: 1. What is the nature and dynamics of water energy nexus? How has this dynamics evolved over the past few decades in India? 1. How shall this dynamics evolve in future under a Business-as- Usual (BAU) scenario for India? What would be the implications for sustainable national development? 2. How shall global climate change affect this dynamics? What policies and measures shall integrate the water - energy - climate change responses with sustainable national development? To address these questions, an integrated modeling framework is developed. Besides secondary data sources from strategic and modeling databases, selected case studies and project specific data was used to augment the database. The long-term assessment {till 2050) is conducted using a scenario-based approach, by integrating and augmenting the existing bottom-up energy systems mode! at the national level and an energy accounting model at the city level. The analysis reinforces the agriculture sector domination in the total water energy nexus (energy for water), underscored by sluggish growth in expanding surface irrigation. In the domestic sector, the increasing rate of urbanization is the main driver of the nexus while increased industrial output has intensified the nexus in the industrial sector. On the other hand, growth in the hydro power sector (water for energy) has been slow vis-à-vis the potential identified. The bottom-up energy systems modeling analysis shows that development along the Business-As-Usual (BAU) path is expected to bring about little improvement (up to 2050) in energy use for water with respect to total energy use. In the context of this research, sustainable national development is assessed in terms of energy usage for water and water use for energy. It is found that the water-energy nexus is progressively energy resource intensive and although hydro power growth would increase in absolute terms, but the overall share of electricity generated would reduce (5% of the total electricity generated in 2050). City analysis, through a case study of Ahmedabad, reinforces the energy re source intensiveness for water along the BAU path. This trend is underscored by increased water demand across all sectors (due to increasing population, increased industrial and commercial activity and expanding city limits), despite significant improvement in energy intensities. The globally agreed long-term climate stabilization target is to limit the temperature rise within 2 degree Celsius which is assumed to be the target to assess future water-energy-climate change nexus in this research. The research though examines other scenarios reported in the literature. Results from scenario analysis show that there would be a reduction in the electricity demand for water across all sectors, significantly more In the scenario around the 'sustainability' framework. This scenario results show a continuous improvement in the intensity of energy usage for water (improve at the rate of 5.34% CAGR for the period 2005-2050) and that this energy demand being increasingly met from hydro power sources (27% of electricity generated in 2050), facilitated by increased South Asia energy cooperation. Thus policies focusing on facilitating demand transitions, end- use efficiency improvements, im-proved urban planning, recycling measures and hydro power growth align the water - energy - cli¬mate change nexus favorably with sustainable national development. Energy accounting modeling analysis at the city level, for Ahmedabad city, uses the target of limiting C02 emissions to the base year (2005) level or below. The scenarios in this context, however; incorporate water- climate change assessment re¬ported in literature. The model results show that the favorable alignment of the water-energy- climate change nexus is facilitated by focusing on policies aimed at energy intensity improvements. Specific policies, in the context; are aimed at demand reduction, energy efficiency improvement and integrated urban planning. This city level modeling exercise is used to delineate policies that are considered in the as¬sessment of the water energy - climate change nexus at the na¬tional level. The key methodological contributions of this research include integration of the water-energy climate change dimensions in an integrated policy modeling frame -work and construction of national and city level databases for water-energy sector. The key pol icy contribution of the research is the delineation of a policy road map to address the water- energy - climate change issues in an integrated manner. The inte¬grated assessment framework and tools and databases delveoped in the research and their applications would be of interest to researchers as well as policy analysts interested in the conceptual and methodological re¬search in the area of integrated policy assessment