There has been a renaissance in the study of borders during the past two decades, partially resulting from the creation of a counter narrative to notions of a borderless world which have been advanced as part of globalization theory. This is reflected in a large number of international workshops and conferences, the BRIT (Border Regions in Transition) network of scholars , IBRU (the International Boundaries Research Unit) at the University of Durham, UK, the Association of Borderland Scholars (ABS) in the USA , and the founding of smaller border research centres at Nijmegen (Holland) , Queens University (Belfast) , to name but a few. The Journal of Borderland Studies deals exclusively with border related material, while other international journals such as, Geopolitics, and Political Geography , publish material dealing with the changing significances and functions of borders in the contemporary world.
Leading scholars in the contemporary study of borders include Anssi Paasi (University of Oulu, Finland), Henk van Houtum (Nijmegen University, Netherlands), Doris Wastl Water (University of Bern, Switzerland), David Newman (Ben Gurion University, Israel), Emanuel Brunet Jailly (University of Victoria, Canada), Irasema Coronado (University of Texas at El Paso).
For the purposes of border control, airports and seaports are also classed as borders. 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 which 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.
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.
Human economic traffic across borders (apart from kidnapping), may involve mass commuting between workplaces and residential settlements. The removal of internal barriers to commerce, as in France after the French Revolution or in Europe since the 1940s, de-emphasises border-based economic activity and fosters free trade.
In much of Europe, such controls were abolished by the Schengen Agreement and subsequent European Union legislation. Since the Treaty of Amsterdam, the competence to pass laws on crossing internal and external boders within the European Union and the associated Schengen States (Iceland, Norway, Switzerland, and Liechtenstein) lies exclusively within the jurisdiction of the European Union, except where states have used a specific right to opt-out (United Kingdom and Ireland, which maintain a common travel area amongst themselves). For details, see Schengen Agreement.
The United States has notably increased measures taken in border control on the Canada–United States border and the United States–Mexico border during its War on Terrorism. The 3600-km (2000-mile) US-Mexico border is probably "the world's longest boundary between a First World and Third World country.
Historic borders such as the Great Wall of China, the Maginot Line, and Hadrian's Wall have played a great many roles and been marked in different ways. While the stone walls, the Great Wall of China and the Roman Hadrian's Wall in Britain had military functions, the entirety of the Roman borders were very porous, a policy which encouraged Roman economic activity with its neighbors. On the other hand, a border like the Maginot Line was entirely military and was meant to prevent any access in what was to be World War II to France by its neighbor, Germany.