Most countries have some form of border control to restrict or limit the movement of people, animals, plants, and goods into or out of the country. Under international law, each country is generally permitted to define the conditions that have to be met by a person to legally cross its borders by its own laws, and to prevent persons from crossing its border when this happens in violation of those laws. In order to cross borders, the presentation of passports and visas or other appropriate forms of identity document is required by some legal orders.

To stay or work within a country's borders aliens (foreign persons) may need special immigration documents or permits that authorise them to do so. Having such documents (i.e. visa and passport) however does not automatically guarantee that the alien will be allowed to cross to the other side of the border. Moving goods across a border often requires the payment of excise tax, often collected by customs officials. Animals (and occasionally humans) moving across borders may need to go into quarantine to prevent the spread of exotic or infectious diseases. Most countries prohibit carrying illegal drugs or endangered animals across their borders. Moving goods, animals or people illegally across a border, without declaring them, seeking permission, or deliberately evading official inspection constitutes smuggling.

As the borders of the territory divided into different countries, the border there are two fundamental characteristics:

(1) geographical features. As human beings living in space on the Earth's surface, thus, the existence of different social or organizational division of open space which has a natural geographic feature the line first, whether it is mountain ranges, rivers, lakes as a demarcation line, or to warp, weft as the dividing line, the performance of geographical features are borders. Geographical characteristics of the boundary description of such borders have some objectivity, though the borders between countries separated in preparation and has a subjective and arbitrary, its between the two countries based on political, economic, military comparison and classification, but also according to population, ethnic, cultural habits and divided, but the border can not exists only in people's minds, it must be reflected in the objective world, that is to be survival of mankind on the earth's surface marked out. Once the boundary marked out, it is objective, naturalness. Surface of the earth or not marked out the borders of the map also not become the border. Of course, due to the limitations of scientific and technological development and historical development of the complex nature of the precise boundary demarcation to bring some difficulties, leading to some countries or between the border demarcation dispute, but to really avoid the countries in the border conflict, the border demarcation to be accurate and objective as possible.

(2) political characteristics. The surface of the earth without borders, only with the establishment of a national human and only after the boundary with the imagine of the earth's surface artificially divided into different areas for each country indicated the scope of the earth's surface. So from the beginning boundary of a political nature, such political expression in two aspects mainly: ? boundary is the boundary of the national implementation of its sovereignty: a country's borders, once established, the country has the right to life of its territory and its The people exercised jurisdiction, without any interference of other countries. As we often say: "Do not interfere in the internal affairs of other countries", their political and geographical significance is not to interfere in matters within the scope of national borders. Otherwise, a violation of the sovereignty. We also often see both sides of the border line of the existence of different political systems, such as the Korean peninsula, north latitude 38 ° near the military demarcation line to the north of the implementation of the socialist system, while in the military demarcation line to the south implementation of the capitalist system. Therefore, we can say that the limits of national sovereignty boundary line. ? is to ensure that the territorial boundary and then to ensure national stability and the natural basis of existence: the borders of a country unstable, bound to affect its relations with neighboring countries, such as the United States and Mexico often Yingelande River diversion dispute India and Bangladesh on the Ganges water, often conflict with the allocation of the. Therefore, we can say that the political characteristics of the boundary is the primary feature.