Algeciras is a port city in the south of Spain, near the city of Gibraltar, slightly to the north than Tarifa, which is the southernmost town of the country. Both cities are situated on the Strait of Gibraltar; Algeciras also faces the Mediterranean.

The name Algeciras is derived from the Arabic al-jazeera ("the peninsula", from which Algiers and Al-Jazeera are also derived).

The modern harbour of Algeciras is one of the busiest in the world, with much traffic to and from Africa. There is a regular ferry service to Tangiers (Morocco) and the Spanish enclave of Ceuta. Because many people who pass through stay the night at Algeciras, there are many hotels and hostals. Around the beginning of August, cars with families of Moroccan immigrants living in Europe mass in the haven waiting to embark the ferry to spend their holidays in Morocco.

An important industry is the Cepsa refinery serving tankers in the Algeciras bay. Then the tankers take the fuel to Gibraltar waters to sell it with cheaper taxes.

One of the main bus stops of Algeciras is also just a few dozens metres from the railway station, near Octavius hotel. Many destinations in the region can be reached from this bus stop. However, for certain destinations one needs to catch a bus at a bus stop along the street that leads to the harbour.

From Algeciras, one can visit Tarifa, to see bird migrations, and Gibraltar, only several minutes by bus.

Operation Algeciras was a failed plan conceived by the Argentinian military to send some Montoneros to sabotage the British military facilities in Gibraltar during the Falklands War.