Siege
Whether the battle can be considered true siege warfare is debatable. Under the theories of Erich von Falkenhayn, it is more distinguishable as purely attrition with a coincidental presence of fortifications on the battlefield. When considering the plans of Crown Prince Wilhelm, purely concerned with taking the citadel and not with French casualty figures, it can be considered a true siege. The main fortifications were Fort Douaumont, Fort Vaux, and the fortified city of Verdun itself. The Germans, through the use of huge artillery bombardments, flamethrowers, and infiltration tactics, were able to capture both Vaux and Douaumont, but were never able to take the city, and eventually lost most of their gains. It was a battle that, despite the French ability to fend off the Germans, neither side won. The German losses were not worth the potential capture of the city, and the French casualties were not worth holding the symbol of her defense.
The development of the armored tank and improved infantry tactics at the end of World War I swung the pendulum back in favor of maneuver, and with the advent of Blitzkrieg in 1939, the end of traditional siege warfare was at hand. The Maginot Line would be the prime example of the failure of immobile, post–World War I fortifications. Although sieges would continue, it would be in a totally different style and on a reduced scale.

World War II: The Blitzkrieg of the Second World War truly showed that fixed fortifications are easily defeated by manoeuvre instead of frontal assault or long sieges. The great Maginot Line was bypassed, and battles that would have taken weeks of siege could now be avoided with the careful application of air power (such as the German paratrooper capture of Fort Eben-Emael, Belgium, early in World War II).

The most important siege was the Siege of Leningrad, that lasted over 29 months, about half of the duration of the entire Second World War. The siege of Leningrad resulted in the deaths of some one million of the city's inhabitants. Along with the Battle of Stalingrad, the siege of Leningrad on the Eastern Front was the deadliest siege of a city in history. In the west, apart from the Battle of the Atlantic, the sieges were not on the same scale as those on the European Eastern front; however, there were several notable or critical sieges: the island of Malta, for which the population won the George Cross and Tobruk. In the South-East Asian theatre, there was the siege of Singapore, and in the Burma campaign, sieges of Myitkyina, the Admin Box, Imphal, and Kohima, which was the high-water mark for the Japanese advance into India.
The Siege of Sevastopol saw the use of the heaviest and most powerful individual siege engines ever to be used: the German 800 mm railway gun and the 600 mm siege mortar. Though a single shell could have disastrous local effect, the guns were susceptible to air attack in addition to being slow to move.

Airbridge: Throughout the war both the Western Allies and the Germans tried to supply forces besieged behind enemy lines with ad-hoc airbridges. Sometimes these attempts failed, as happened to the besieged German Sixth Army the Battle of Stalingrad, and sometimes they succeeded as happened during the Battle of the Admin Box (5 – 23 February 1944) and the short Siege of Bastogne (December 1944).
The logistics of strategic airbridge operations were developed by the Americans flying military transport aircraft from India to China over the Hump (1942–1945), to resupply the Chinese war effort of Chiang Kai-shek, and to the USAAF XX Bomber Command (during Operation Matterhorn).
Tactical airbridge methods were developed and, as planned, used extensively for supplying the Chindits during Operation Thursday (February – May 1944). The Chindits, a specially trained division of the British and Indian armies, were flown deep behind Japanese front lines in the South-East Asian theatre to jungle clearings in Burma where they set up fortified airheads from which they sailed out to attack Japanese lines of communications, while defending the bases from Japanese counterattacks. The bases were re-supplied by air with casualties flown out by returning aircraft. When the Japanese attacked in strength the Chindits abandoned the bases and either moved to new bases, or back to Allied lines.

Post-World War II: Several times during the Cold War the western powers had to use their airbridge expertise.

The Berlin Blockade from June 1948 to September 1949, the Western Powers flew over 200,000 flights, providing to West Berlin up to 8,893 tons of necessities each day.
Airbridge was used extensively during the Battle of Dien Bien Phu during the First Indochina War, but failed to prevent its fall to the Việt Minh in 1954.
In the next Vietnam War, airbridge proved crucial during the siege of the American base at Khe Sanh in 1968. The resupply it provided kept the North Vietnamese Army from capturing the base.
In both Vietnamese cases, the Viet Minh and NLF were able to cut off the opposing army by capturing the surrounding rugged terrain. At Dien Bien Phu, the French were unable to use air power to overcome the siege and were defeated. However, at Khe Sanh, a mere 14 years later, advances in air power—and a reduction in Vietnamese anti-aircraft capability—allowed the United States to withstand the siege. The resistance of US forces was assisted by the PAVN and PLAF forces' decision to use the Khe Sanh siege as a strategic distraction to allow their mobile warfare offensive, the first Tet Offensive, to unfold securely.
The Battle of Khe Sanh displays typical features of modern sieges, as the defender has greater capacity to withstand the siege, the attacker's main aim is to bottle operational forces or create a strategic distraction, rather than take the siege to a conclusion.
In neighboring Cambodia, at that time known as the Khmer Republic, the Khmer Rouge used siege tactics to cut off supplies from Phnom Penh to other government-held enclaves in an attempt to break the will of the government to continue fighting.
In 1972, during the Easter offensive, the siege of An Lộc Vietnam occurred. ARVN troops and U.S. advisers and air power successfully defeated communist forces. The Battle of An Lộc pitted some 6,350 ARVN men against a force three times that size. During the peak of the battle, ARVN had access to only one 105 mm howitzer to provide close support, while the enemy attack was backed by an entire artillery division. ARVN had no tanks, the NVA communist forces had two armoured regiments. ARVN prevailed after over two months of continuous fighting. As General Paul Vanuxem, a French veteran of the Indochina War, wrote in 1972 after visiting the liberated city of An Lộc: "An Lộc was the Verdun of Vietnam, where Vietnam received as in baptism the supreme consecration of her will."
During the 1982 Lebanon War, the Israel Defence Forces besieged Beirut, the capital of Lebanon, to quickly realize their goals including the eviction of the Palestine Liberation Organization from the country.
During the Yugoslav Wars in the 1990s, Republika Srpska forces besieged Sarajevo, the capital of Bosnia-Herzegovina. The siege lasted from 1992 until 1996.
Numerous sieges haven taken place during the Syrian Civil War, such as the Siege of Homs, Siege of Kobanî, Siege of Deir ez-Zor (2014–2017), Siege of Nubl and al-Zahraa, and Siege of al-Fu'ah and Kafriya.
Multiple sieges took place in the 2022 Russian invasion of Ukraine, most notably the Siege of Mariupol.
The Israel–Hamas war in 2023-2024 contained multiple sieges, including the Siege of Gaza City and the Siege of Khan Yunis.

Police sieges: Siege tactics continue to be employed in police contexts; such a siege is typically called a standoff or, in law enforcement jargon, a barricade situation. Standoffs may result from crimes and incidents such as robberies, raids, search and arrest warrants, prison riots, or terrorist attacks. Standoffs occur due to a variety of factors, most prominently the safety of police (against whom the besieged may have the upper hand), the besieged suspects (who police generally intend to arrest), bystanders (who may be in the crossfire), and hostages (who may be injured or killed by the suspects).
The optimal result of most standoffs is a peaceful resolution: the safe extraction of hostages and bystanders, and the peaceful surrender and arrest of the hostage-takers. To ensure this, police make use of trained negotiators and psychologists to learn the hostage-takers' demands (and meet said demands if feasible or permissible), gain the hostage-takers' trust, clarify that police do not intend to kill them or will even let them go (regardless of whether such claims are true), and coax the hostage-takers into surrendering or at least releasing hostages. In the event a peaceful resolution is impossible—negotiations fail or do not proceed, hostages are released but the hostage-takers refuse to surrender, the hostage-takers resist violently, or hostages are killed—police may respond in force, generally being able to rely on police tactical units or even military support if possible and required.