Idanha-a-Nova (Portuguese pronunciation: [iˈðɐɲa ˈnɔvɐ]) is a municipality in the district of Castelo Branco in east-central Portugal. The population in 2011 was 9,716, in an area of 1416.34 km², making it one of the largest municipalities in Portugal. The municipal holiday is the Monday 15 days after Easter.
Idanha-a-Nova has hosted the massive biannual Boom Festival since 2002, during which the population of the community temporarily increases more than fivefold. The present mayor is Álvaro José Cachucho Rocha, representing the Socialist Party.