The present Mayor is Manuel Coelho Carvalho, elected by the Unitarian Democratic Coalition. The President of the Municipal Assembly is Francisco do Ó Pacheco, also elected by the Unitarian Democratic Coalition.
The town has a long history going back to Roman times (then called Sinus). The castle on the cliff was built under King Pedro, started in 1362.
Until the early 1970s it was a sheltered fishing village with a long history of commercial relations with cities from the Mediterranean. Its large marina, along a breakwater, is the only marina between Setúbal and the Algarve.
The town is now rapidly expanding by the presence of its deep-sea port and industrial platform.
The municipal holiday is November 24. Every Summer, the town hosts the FMM Sines - Festival Músicas do Mundo, a world music festival that brings thousands of enthusiasts and musicians from all continents.
The town has also a very heterogeneous population, since it received a large amount of refugees from the Portuguese overseas colonies in the late 1970s. Foreign workers of the port and the petrochemical industry also add to this.
Even though the north of the district has an important industrial presence, the town itself preserves plenty of historical landmarks and its privileged location, sitting on a cliff in front of a small bay, provides beautiful views to the Atlantic.
The nearby village of Porto Covo attracts many tourists thanks to its preserved coastline and the beauty of the traditional buildings.
The municipality has an important investment park, managed by AICEP Global Parques.
The municipality is composed of two parishes :