The only condition for you to gain entry into another country is the possession of a valid visa. On the other hand, there are also various exemption schemes that can also grant you entry into another country as well. Visa-free entry may be granted to those who have diplomatic passports in some cases just as normal passport holders even require visas.
However, various countries have mutual agreements such that under certain conditions, a visa is not required. For example, if the visit is for tourism and for a relatively short duration. Such mutual agreements may be as a result of being member of a shared heritage or international organizations.
According to the visa exemption schemes and agreements, if you are a citizen of the European Union member countries, you are eligible to travel to and stay in all other EU countries without a visa.
Likewise, the Visa Waiver Program of the United States permits citizens of 36 countries to travel to the USA devoid of visa. Since the US does not allow visa-free entry to citizens of some countries that permit US citizens visa-free entry, this scheme is not mutual, although some countries that are not in the waiver program of the US require the Unites States of America citizens to pay a charge equivalent to paying the US visa fee to gain entry to their country.
Citizens of any Gulf Cooperation Council can enter and stay for as long as necessitated in any other Gulf Cooperation Council member state. Not only that, all members Economic Community of West African States – ECOWAS citizens with the exemption of those defined as undesirable aliens by law, may enter and stay without a visa in any member state for at least 90 days. Valid travel document and international vaccination certificate are the only requirement.
Furthermore, you don’t need visas for entry into any of the member states, if you are nationals of the East African Community member states. At the same time, quite a number of countries in the Commonwealth do not need tourist visas of citizens of other Commonwealth countries to gain entry.
As a result of the Indo-Nepal friendship treaty of 1951, India and Nepal permit their citizens to enter, live and work in each other’s countries. In addition, to travel to Bhutan by Indians does not need visa but just to get passes at the border checkpoints.
Also, apart from Burma where its citizens are necessitated to have a visa to enter seven out of the ten states, citizens of member states of the Association of Southern Asian Nations do not need tourist visas to visit another member state. Singapore, Philippines and Indonesia are the exceptions.
CIS – Commonwealth of Independent States member states jointly permit their citizens to enter visa-free for short stays, at least. However, exceptions exist between Armenia and Azerbaijan as well as Tajikistan and Uzbekistan.
In order to promote business, facilitate tourism or even to just cut expenses on maintaining consular posts abroad, other countries may unilaterally grant visa-free entry to nationals of certain countries.