Gibraltar, colloquially known as The Rock, (or simply 'Gib'), is an overseas territory of the United Kingdom with a 2004 population of approximately 27,800 people. It sits at the entrance to the Mediterranean Sea, and is bordered by Spain to the north. The people of Gibraltar are British citizens.
Gibraltar is not part of the Schengen Area or the EU. This means that there are immigration and customs controls when traveling between Spain and Gibraltar. Citizens of the European Union are required to have a national identity card or passport, while all others are required to have a passport to enter. The entry requirements for Gibraltar are not the same as the United Kingdom. Unless exempt from visa requirements, to enter Gibraltar you must have either a Gibraltar visa (to be applied for separately from a normal British visa at a British embassy/consulate), a UK visa valid for at least one year, or a UK permit of residence valid for at least 5 years. If arriving by air, Gibraltar airport staff will refuse entry to anyone who does not comply with these requirements.
Although entry into Gibraltar will technically invalidate a single-entry Schengen visa, in practice passports are checked but not stamped on entry by land, and those with single-entry visas usually get re-admitted to Spain without any problems.
After crossing customs, you may be asked to cross the airfield, being absolutely exposed to planes. DO NOT behave differently in this area. Sometimes, if you are on a tour you can stay on the vehicle and citizens using cars can cross by car.
