A visa  (short for the Latin carta visa, lit. "the document having been seen") is a permit given by a country that allows someone to go to that country. A visa is a document that is stamped on a person's passport by an embassy. It names the kind of visit and says how long the person can stay. Sometimes, people need to go through an interview held at the embassy before they get a visa.

Many countries require foreign visitors to have a valid passport and a visa before they can enter the country, but there are exceptions (see below for examples of such these).

Visas are associated with the request for permission to enter (or exit) a country, and are thus, for some countries, not the same as actual formal permission for an alien to enter and remain in the country.

Some countries, such as some states of the former Soviet Union, require that their citizens, and sometimes foreign travelers, obtain an exit visa in order to be allowed to leave the country. Until 2004, foreign students in Russia were issued only an entry visa on being accepted to University there, and had to obtain an exit visa to return home.  This policy has since been changed, and foreign students are now issued multiple entry (and exit) visa.

Conditions of issue 
Some visas can be granted on arrival or by prior application at the country's embassy or consulate, or sometimes through a specialized travel agency with permission from the issuing country in the country of departure. If there is no embassy or consulate in one's home country, then one would have to travel to a third country (or apply by post) and try to get a visa issued there. The need for a visa generally depends on the citizenship of the applicant, how long the applicant plans to stay, and the activities that the applicant may wish to do in the country he visits. These may result different formal categories of visas, with different issue conditions.

Some, but not all, countries have reciprocal visa regimes: if Country A requires citizens of Country B to have a visa to travel there, then Country B may apply reciprocity and require a visa from citizens of Country A.  Likewise, if A allows B's citizens to enter without a visa, B may allow A's citizens to enter without a visa.

Examples of such reciprocal visa regimes are between:
 Algeria  and Canada  
 most CIS member states and African countries
 Brazil and Canada/CIS member states
 Armenia and most non-CIS member states 

A fee may be charged for issuing a visa; these are typically also reciprocal, so if country A charges country B's citizens 50 USD for a visa, country B will often also charge the same amount for country A's visitors. The fee charged may also be at the discretion of each embassy. A similar reciprocity often applies to the duration of the visa (the period in which one is permitted to request entry of the country) and the number of entries one can attempt with the visa. Expedited processing of the visa application for some countries will generally incur additional charges.

This reciprocal fee has become more common in recent years with the decision of the United States to charge nationals of various countries a $100 visa processing fee (non-refundable, even if a visa is not issued).  A number of countries, including Brazil, Chile, and Turkey have reciprocated.  Brazil requires an advance visa before entry into the country, and that a US citizen be fingerprinted and photographed on arrival—matching U.S. requirements for Brazilians and other foreigners.

The issuing authority, usually a branch of the country's foreign ministry or department (e.g. U.S. State Department), and typically consular affairs officers, may request appropriate documentation from the applicant. This may include proof that the applicant is able to support himself in the host country (lodging, food), proof that the person hosting the applicant in his or her home really exists and has sufficient room for hosting the applicant, proof that the applicant has obtained health and evacuation insurance, etc. Some countries ask for proof of health status, especially for long-term visas; some countries deny such visas to persons with certain illnesses, such as AIDS.  The exact conditions depend on the country and category of visa.  Notable examples of countries requiring HIV tests of long-term residents are Russia  and Uzbekistan.   However, in Uzbekistan, the HIV test requirement is sometimes not strictly enforced. 

Developed countries frequently demand strong evidence of intent to return to the home country, if the visa is for a temporary stay, and especially if the applicant is from a developing country, due to immigration concerns.

The issuing authority may also require applicants to attest that they have had no criminal convictions, or that they do not partake in certain activities (like prostitution or drug trafficking).  Some countries will deny visas if the travellers' passports show evidence of citizenship or travel to a country which is not recognized by that country.  For example, Saudi Arabia will not issue visas to nationals of Israel or those with evidence of visiting Israel.

Types of visa 

Common types of visas are:
 A transit visa, usually valid for 3 days or less, for passing through the country to a third destination.
 A tourist visa, for a limited period of leisure travel, no business activities allowed.  Some countries do not issue tourist visas. Saudi Arabia introduced tourist visas only in 2004 although it did (and still does) issue pilgrimage visas for Hajj pilgrims.
 A business visa, for engaging in commerce in the country. These visas generally preclude permanent employment, for which a work visa would be required.
 A temporary worker visa, for approved employment in the host country. These are generally more difficult to obtain but valid for longer periods of time than a business visa. Examples of these are the United States' H-1B and L-1 visas.
 A visa on arrival, which is a visa granted immediately prior to entering the country, such as at an airport or border control post. This is distinct from not requiring a visa at all, as the visitor must still obtain the visa before they can even try to pass through immigration. The on-arrival visa usually is nothing more than an arrival tax, though the visitors can still be denied entry even with a visa.
 A spousal visa, granted to the spouse of a resident or citizen of a given country, in order to enable the couple to settle in that country.  Examples include the United Kingdom's EEA family permit.

Less common visas include:
 A student visa, which allows its holder to study at an institution of higher learning in the issuing country.  Students studying in Algeria, however, are issued tourist visas. 
 A working holiday visa, for individuals traveling between nations offering a working holiday programme, allowing young people to undertake temporary work while traveling. At least ten European countries allow work for non-EU students.

 A diplomatic visa (sometimes official visa), which confers diplomatic status on its holder and is normally only available to bearers of diplomatic passports.
 A courtesy visa issued to representatives of foreign governments or international organizations who do not qualify for diplomatic status but do merit expedited, courteous treatment. A courtesy visa does not normally confer privileges or immunities.
 A journalist visa, which some countries require of people in that occupation when travelling for their respective news organizations. Countries which insist on this include Cuba, Iran, North Korea, Saudi Arabia, the United States (I-visa ) and Zimbabwe.
 Afiancee visa, granted for a limited period prior to intended marriage based on a proven relationship with a citizen of the destination country. For example, a German woman who wishes to marry an American man would obtain a Fiancee Visa (also known as a K-1 visa) to allow her to enter the United States.
 An immigrant visa, granted for those intending to immigrate to the issuing country.  They usually are issued for a single journey as the holder will, depending on the country, later be issued a permanent resident identification card which will allow the traveller to enter to the issuing country an unlimited number of times. (for example, the United States Permanent Resident Card)...

Entry and duration period 

Visas can also be single-entry, which means the visa is cancelled as soon as the holder leaves the country, double-entry, or multiple-entry, permitting multiple entries into the country with the same visa. Countries may also issue re-entry permits that allow temporarily leaving the country without invalidating the visa.  Even a business visa will normally not allow the holder to work in the host country without an additional work permit.

Once issued, a visa will usually have to be used within a certain period of time.

The validity of a visa is not the same as the authorized period of stay in the issuing country. The visa validity usually indicates when the alien can apply for entry to the country.  For example, if a visa has been issued January 1st and expires March 30th, and the typical authorized period of stay in a country is 90 days, then the 90-day authorized stay starts on the day the passenger reaches the country, which has to be between January 1st and March 30th. The traveller could therefore stay in the issuing country until June 1st.    

Once in the country, the validity period of a visa or authorized stay can often be extended for a fee if the immigration authorities choose to do so.  Staying longer than the period of authorized stay given by the immigration officers is considered illegal immigration even if the visa validity period is not over (i.e. for multiple entry visas) and a form of being "out of status" and the offender may be fined, prosecuted, deported, or even blacklisted (banned) from entering the country again.  

Entering a country without a valid visa or visa exemption may result in being arrested and removed (deportation or exclusion) from the country. Doing things that are not authorized by the status of entry (for example, working while having a non-worker tourist status) can result in the individual being deemed removable, in common speech an illegal alien. Such violation is not a violation of a visa, despite the common misuse of the phrase, but a violation of status, hence the term "out of status."

Even having a visa does not guarantee that somebody can enter ah ost country. The border crossing authorities make the final determination to allow entry, and may even cancel a visa at the border if the alien cannot demonstrate to their satisfaction that they will abide by the status their visa grants them.

Visa and immigration laws may be very different among countries.  As such, aliens are advised to check with immigration lawyers for visa and immigration laws governing the countries they wish to enter and eligibility to receive visas or other immigration benefits.

Visa extensions 

Many countries have a mechanism to allow the holder of a visa to apply to stay longer in that country. For example, in Denmark a visa holder can apply to the Danish Immigration Service for a Residence Permit after they have arrived in the Country. In the United Kingdom applications can be made to the Border and Immigration Agency. In certain circumstances, it is not possible for the holder of the visa to do this, either because the country does not have a mechanism to prolong visas or, most likely, because the holder of the visa is using a short stay visa to live in a country. In such cases, the holder often engages in what is known as a visa run; leaving the country for a short period in order to apply for a new visa prior to their return or so that they can be given a fresh permission to stay when they re-enter.

Visa refusal 
A visa may be denied for a number of reasons, including (but not limited to) if the applicant:
 has committed fraud or misrepresentation in his or her application;
 cannot prove to have strong ties to their current country of residence;
 intends to permanently live or work in the country she/he will visit;
 does not have a legitimate reason for the journey;
 has no clear way of having enough resources to take care of himself/herself while in the country;
 does not have accommodation in the destination country;
 has not arranged his or her transportation;
 does not have a health/travel insurance valid for the destination and the duration of stay;
 has a criminal record or has criminal charges pending;
 does not have a good moral character;
 wants to get a visa too soon;
 is considered to be a security risk;
 had their previous visa application(s) rejected;
 is a citizen of a country with whom the host country has poor or non-existent relations;
 has a contagious disease, such as tuberculosis;
 has previous immigration violations;
 has never undertaken any foreign travel before;
 has traveled before, but taken visas for other countries which are nowhere near the destination country;
 unable to demonstrate basic local language skills;
 has planned a vacation for no particular purpose other than sightseeing.
 has a passport that expires too soon

Visa exemption schemes 
Possession of a valid visa is a condition for entry into many countries, however various exemption schemes do exist. In some cases visa-free entry may be granted to holders of diplomatic passports even as visas are required by normal passport holders (see: Passport).

Some countries have reciprocal agreements such that a visa is not needed under certain conditions, e.g. when the visit is for tourism and for a relatively short period. One example of this is the Visa Waiver Program of the United States. Such reciprocal agreements may stem from common membership in international organizations or a shared heritage:
 All citizens of ECOWAS member states, excluding those defined by law as undesirable aliens, may enter and stay without a visa in any member state for a maximum period of 90 days. The only requirement is a valid travel document and international vaccination certificates.
 Nationals of the East African Community member states do not need visas for entry into any of the member states.
 Some countries in the Commonwealth do not require tourist visas for citizens of other Commonwealth countries.
 Most countries in the Association of Southeast Asian Nations (ASEAN) do not require tourist visas for citizens of other ASEAN countries.
 Armenia  and Uzbekistan  allows citizens of CIS member states, except Turkmenistan, to enter visa-free as tourists.
Other countries may also unilaterally grant visa-free entry to nationals of certain countries in order to facilitate tourism.

Visa-free travel between countries also occurs in all cases where passports are not needed for such travel. 
(For examples of passport-free travel, see International travel without passports.)

Common visas 
Normally, visas are valid for entry only into the country which issued the visa. Countries that are members of regional organizations or party to regional agreements may however issue visas valid for entry into some or all of the member states of the organization or agreement:

 the Schengen Visa may be the best-known example of a common visa. This visa has it origins in the 1985 Schengen Agreement among European states which allows for a common policy on the temporary entry of persons (including visas). The visa allows a tourist or visitor access to the area covered by the agreement (known as the “Schengen area” or “Schengenland”). Citizens of non-EU, non-EEA countries who wish to visit Europe as tourists, and who require a visa to enter the Schengen area, are simply required to get only the common Schengen Visa from the Embassy/Consulate of any of the Schengen countries. After this, they may visit any or all of the Schengen countries as tourists or for business without hindrance. They are not required to get separate visas for all the Schengen countries they wish to visit.

 the CARICOM Visa was introduced in late 2006 and allowed visitors to travel between 10 CARICOM member states (Antigua & Barbuda, Barbados, Dominica, Grenada, Guyana, Jamaica, St. Kitts & Nevis, St. Lucia, St. Vincent & the Grenadines and Trinidad & Tobago). These 10 member countries had agreed to form a "Single Domestic Space" in which travellers would only have their passport stamped and have to submit completed, standardized entry and departure forms at the first port and country of entry. The CARICOM Visa was applicable to the nationals of all countries except CARICOM member states (other than Haiti) and associate member states, Canada, France, Germany, Ireland, Italy, Japan, the Netherlands, South Africa, the United Kingdom, the United States of America and the overseas countries, territories or departments of these countries. The CARICOM Visa could be obtained from the Embassies/Consulates of Barbados, Jamaica and Trinidad & Tobago and in countries which have no CARICOM representatives, the applications forms could be obtained from the Embassies/Consulates of the United Kingdom. The common visa was only intended for the duration of the Cricket World Cup and was discontinued on May 15, 2007. However, discussions are ongoing into instituting a revised CARICOM visa on a permanent basis in the future.

 the Central American Single Visa (Visa Única Centroamericana) was implemented by the CA-4 agreement between Guatemala, El Salvador, Honduras, and Nicaragua. It is required for citizens of all other countries, eliminating the need for separate entry visas for each of the countries. Persons entering the region on Type "B" visas can enter the area through any Port of Entry. Persons entering on Type "C" visas (issued through prior consultation with the Ministry of Foreign Affairs) must enter through a Port of Entry in the country that issued the visa. Once a person has been admitted, they may travel onto any of the other countries and are allowed to stay through the date authorized at the original Port of Entry.

 An East African Single Tourist Visa has been up for approval by the relevant sectoral authorities under the East African Community (EAC) integration programme. The visa would be valid for all three partner states in the EAC (Kenya, Tanzania and Uganda). Under the proposal for the visa, any new East African single visa can be issued by any partner state's embassy. The visa proposal followed an appeal by the tourist boards of the partner states for a common visa to accelerate promotion of the region as a single tourist destination and the EAC Secretariat wants it approved before November's World Travel Fair (or World Travel Market) in London. When approved by the East African council of ministers, tourists could apply for one country's entry visa which would then be applicable in all regional member states as a single entry requirement initiative.

 The SADC UNIVISA (or Univisa) has been in development since SADC members signed a Protocol on the Development of Tourism in 1998. The Protocol outlined the Univisa as an objective so as to enable the international and regional entry and travel of visitors to occur as smoothly as possible. It was expected to become operational by the end of 2002. Its introduction was delayed and a new implementation date, the end of 2006, was announced. However, the SADC now aims to have the univisa system in place by 2008, before the 2010 FIFA World Cup in South Africa. The univisa was originally intended to only be available, initially, to visitors from selected “source markets” such as Australia, the Benelux countries, France, Germany, Italy, Japan, Portugal, Spain, the United Kingdom and the USA. It is now expected that when the Univisa is implemented, that it will apply to non SADC international (long-haul) tourists travelling to and within the region and that it will encourage multi - destination travel within the region. It is also anticipated that the univisa will unlock the tourism potential of transfrontier parks by lowering the boundaries between neighbouring countries in the parks. The visa is expected to be valid for all the countries with transfrontier parks (Botswana, Lesotho, Mozambique, Namibia, South Africa and Zimbabwe) and some other SADC countries (Angola and Swaziland).

References 

Travel
Identification documents