Viareggio (Italian pronunciation: [vjaˈreddʒo; vi.aˈreddʒo]) is a city and comune in northern Tuscany, Italy, on the coast of the Tyrrhenian Sea. With a population of over 62,000, it is the second largest city within the province of Lucca, after Lucca.

It is known as a seaside resort as well as being the home of the famous carnival of Viareggio (dating back to 1873), and its papier-mâché floats, which (since 1925), parade along the promenade known as "Passeggiata a mare", in the weeks of Carnival. The symbol of the carnival of Viareggio and its official mask is Burlamacco, designed and invented by Uberto Bonetti in 1930.

The city traces its roots back to the first half of the 16th century when it became the only gate to the sea for the Republic of Lucca. The oldest building in Viareggio, known as Torre Matilde, dates back to this time and was built by the Lucchesi in 1541 as a defensive fortification to fight the constant menace of corsair incursions.

Viareggio is also an active industrial and manufacturing centre; its shipbuilding industry has long been renowned around the world and its fishing and floricultural industries are still fundamental sectors to the city's economy.

Viareggio hosts the Premio letterario Viareggio Répaci for literature, established in 1929. Amongst the other events organized around the year, it is worth mentioning the Festival Gaber, which has been held every August since 2004 to celebrate the memory of Giorgio Gaber, and is attended by several high-profile Italian musicians.