The patron saint of Rosignano Marittimo is Saint Nicholas of Tolentino, celebrated on 10 September. Having become a castle, the village was the last Pisan outpost before the Maremma and the seat of a captaincy; after the death of Countess Matilda of Canossa it came under the authority of the Pisan episcopal church, which in 1146 recognised its institutions as a rural commune. Decades of wars against Florence followed, until in 1406 the town became the seat of the Florentine podesteria; dismantled in 1433 after a rebellion, the stronghold was later rebuilt, and some of its towers can still be seen in the old town today.
In the early 20th century, with improved communication routes and the opening of the Livorno-Cecina railway, the rise of the Solvay Group's chemical industry led to the founding of the hamlet of Rosignano Solvay, initially known as «Paese Novo». The municipality's coastline is today also known for the Spiagge Bianche (White Beaches), whose very bright sand is itself a legacy of the area's industrial processing.
