A border barrier, border fence or border wall is a separation barrier that runs along or near an international border. Such barriers are typically constructed for border control purposes such as curbing illegal immigration, human trafficking, and smuggling.^[1][2] Some such barriers are constructed for defence or security reasons. In cases of a disputed or unclear border, erecting a barrier can serve as a de facto unilateral consolidation of a territorial claim that can supersede formal delimitation. A border barrier does not usually indicate the location of the actual border, and is usually constructed unilaterally by a country, without the agreement or cooperation of the other country.

Examples of border walls include the ancient Great Wall of China, a series of walls separating China from nomadic empires to the north. The construction of border barriers increased in the early 2000s; half of all the border barriers built since World War II which ended in 1945, were built after 2000.^[3]

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• Buffer zone
• Canada–United States border
• Canal
• Citadel
• Defense line
• Peace lines
• Demilitarised zone
• Defensive walls
• List of cities with defensive walls
• List of fortifications
• List of walls
• Second Amendment sanctuary
• Trump wall
• Fences in Rio de Janeiro