After weeks of indecision, Germany has announced it will send Leopard 2 tanks to Ukraine and allow other countries to do the same.
Ukraine has pleaded for months for Western nations to send modern tanks to give its forces the firepower they need to retake territory occupied by Russia.
Kyiv is widely expected to mount another counteroffensive in the spring after hugely successful drives last year that seized big chunks of territory around Kharkiv in the east and liberated Kherson in the south.
Volodymyr Zelenskyy, the Ukrainian president, says his forces need more and heavier weapons - in particular Western tanks - to push the Russians back.
After the UK led the way in promising 14 of its Challenger 2 tanks, Germany has now agreed to send 14 of its own Leopard 2 tanks as well as authorise other countries to do the same as it owns the export licence.
The US is understood to be preparing to announce that it will supply Kyiv with a number of its M1 Abrams tanks - perhaps as part of an agreement with Berlin.
So what are the Leopard 2, M1 Abrams and Challenger 2 tanks, and which other Western armoured vehicles are being sent to Ukraine?
Leopard 2 - Germany's main battle tank used by various NATO countries
Ukraine has long urged the West to send tanks to help its forces fight Russia, and at the top of the list has been the Leopard 2.
Considered a main battle tank in the same way as the Challenger 2 and first introduced in 1979, it offers good protection against armour-piercing rounds and anti-tank guided weapons.
It has been reported that the Leopard 2 was estimated to be able to penetrate frontal armour of the Soviet-made T-72 tank from 2,000 metres away and that of the T-62 from more than 4,000 metres - both of which are in use by the Russian military in Ukraine.
M1 Abrams: Highly manoeuvrable but poor fuel efficiency
After weeks of discussion, the Biden administration is preparing to send Abrams tanks to Ukraine, according to three senior US officials.
It has a 1,500-horsepower turbine engine - notoriously low on fuel efficiency - and a 120mm main gun.
The tank can make a difference on the battlefield through "lethal firepower, unparalleled survivability, and audacious manoeuvre", the US army says.
Any agreement to supply Ukraine with Abrams tanks is likely to be perceived as an effort to persuade Germany to authorise donation of the Leopard 2, which uses less fuel and is widely available in Europe.
Challenger 2: British tank buster that has 'never' been destroyed
The British Challenger 2 is a main battle tank that has been used on operations in Bosnia and Herzegovina, Kosovo and Iraq.
First introduced into service with the British Army in 1994, a number of Challenger 2s are deployed in Estonia as part of NATO's Enhanced Forward Presence in the Baltic States.
It features a main 120mm rifled gun and has a crew of four - commander, gunner, loader/operator and a driver.
The British Army says it has "never experienced a loss at the hands of the enemy".
Bradley fighting vehicle: Armoured infantry transport from the US
Earlier this month, the White House announced that it will be delivering dozens of its Bradley fighting vehicles to Ukraine as well as hundreds of the anti-tank missiles they can fire.
While not a tank, strictly speaking, Pentagon press secretary Brigadier General Pat Ryder said they provide "a level of firepower and armour that will bring advantages on the battlefield".
Bradleys are armoured vehicles that can transport infantry in combat zones and are often equipped with a 25mm M242 Bushmaster chain gun as their main weapon along with an anti-tank missile system.
Mr Zelenskyy hailed the move: "For the first time, we will get Bradley armoured vehicles - this is exactly what is needed.
"New guns and rounds, including high-precision ones, new rockets, new drones. It is timely and strong."
Marder infantry fighting vehicles from Germany
Before the decision on the Leopards, Germany had said it wanted to deliver around 40 Marder infantry fighting vehicles to Ukraine before the end of March.
Resembling a light tank in some ways, the Marder can carry five or six troops and is one of the largest and heaviest of its type.
Germany has large numbers of Marders in storage and vice chancellor Robert Habeck said Berlin could ultimately send its entire functioning fleet of the weapons.
AMX-10 RC: France's 'light tank' designed for recon missions
The French defence ministry said it will hold talks with its Ukrainian counterpart to arrange for the delivery of armoured combat vehicles.
Designated as "light tanks" in French, the AMX-10 RC carries a 105mm cannon and two machine guns.
It's primarily designed for reconnaissance missions and has enough armour to protect against light infantry weapons, according to the French defence ministry.
It has wheels rather than tracks, allowing it to be more mobile than heavy tanks.