Tehri Dam is located in highly complex geo-tectonic environs of Himalayan region prone to seismic activity. Safe design and construction of Tehri Dam Project, posed immense technical challenges. In such complex environment, a 260.5 m high Earth and Rock-fill dam with slightly inclined clay core has been designed by utilizing locally available fill materials, with little or no processing. Design of the dam has been finalized by involving internationally renowned expert Institutes in the field viz. HPI, Moscow and DEQ, IIT, Roorkee. Extensive surface as well as sub-surface treatment of the core seat foundation i.e. grouting has been done for improving its properties. For monitoring the health of the dam during construction and operation period, a large number of instruments have been installed within the body of dam and its foundation. One of the unique features of this dam is the provision of inspection galleries within the core of the dam through which physical inspection and monitoring of the dam behaviour is possible during the operation period of the project. The paper describes in brief, about Geological and Geotechnical aspects and challenges during construction of the Tehri Hydropower Project.