Castiglione della Pescaia, regionally simply abbreviated as Castiglione, is an ancient seaside town in the province of Grosseto, in Tuscany, central Italy. The modern city grew around a medieval 12th century fortress (Italian: castello) and a large fishery, from which it acquired its designation. Today Castiglione is a very popular tourist destination with attractions that include beaches, natural parks, biking trails, historical Etruscan archaeological sites, a panoramic mediaeval hamlet as well as the natural reserve Diaccia Botrona, a swampy humid environment of historical relevance whose endangered wildlife comprise pink flamingoes, mallards and ducks.

Despite Castiglione's popularity as a holiday destination, the town's natural surroundings - including the sea, marshes and pinewoods typical of the Maremma area - have been meticulously preserved and are today forming protected natural reserves. Notably, in 2015 Castiglione's sea was nominated as Italy's most beautiful by the national non-governmental environmentalist organisation Legambiente, which not only praised the town's seawater cleanliness but also its environmental efforts and efficient recycling.

Castiglione is the most visited seaside destination in Tuscany and it ranks fourth among the most visited cities in the region. In 2019, approximately 1.6 million tourists visited Castiglione reaching an historic record. The town is also one of the most visited in Italy.

Interestingly, Castiglione della Pescaia is home to the second most expensive street in Italy for property prices, with average values exceeding those of homes in every other Italian street except one, also in Tuscany.

Many notable figures have resided or reside in Castiglione and its comune. Among these are Golden Globe-winning actor Roger Moore, Oscar-winning actress Sophia Loren, Grammy-winning conductor Georg Solti, film producer Carlo Ponti, Formula One racing driver Alex Zanardi, authors Italo Calvino, Pietro Citati, and Carlo Fruttero,] film director Giovanni Veronesi, banker Siegmund G. Warburg, and many others, including former Italian prime minister Romano Prodi, also former President of the European Commission, and former King of Spain Juan Carlos I.