Visas are associated with the request for permission to enter a territory and thus are, in most countries, distinct from actual formal permission for an alien to enter and remain in the country. In each instance, a visa is subject to entry permission by an immigration official at the time of actual entry and can be revoked at any time.

Visa evidence most commonly takes the form of a sticker endorsed in the applicant’s passport or other travel document but may also exist electronically. Some countries no longer issue physical visa evidence, instead recording details only in immigration databases.