Viana do Castelo (Portuguese pronunciation: [viˈɐnɐ ðu kɐʃˈtɛlu]) is a municipality and seat of the Viana do Castelo District in the Norte Region of Portugal. The city proper has 36,148 (INE, 2001) inhabitants and the municipality has a total population of 91,238 inhabitants (2006) over a total area of 318.6 km².

It is located at the mouth of the Lima River.