Large amounts of military equipment have been given to Ukraine by more than 30 countries, but in some areas Ukrainian troops have been heavily out-gunned.
Which countries are giving the most?
In terms of overall spending, the US has committed to providing far more than any other individual country.
The UK and Poland have pledged the second and third largest amounts.
The US has announced new assistance worth about $3bn (£2.5bn) - the single largest package since Russia's invasion.
And the UK has also pledged to give a further £54m ($64m) in military aid to Ukraine.
President Zelensky has appealed for more funding, and has said the monthly cost of defence for Ukraine was about $5bn (£4.1bn).
What are the key systems?
Military professionals say success on the battlefield requires a huge range of weaponry, as well as training, spare parts and other support.
"No weapon system is a silver bullet," according to General Mark Milley, US Chairman of the Joint Chiefs of Staff.
However, several weapon systems are believed to have played key roles in the conflict so far.
Long-range rockets
Analysts say Ukraine badly needs better supplies of artillery and ammunition to hold on to key positions.
So far, at least a dozen long-range rocket launchers have been sent to Ukraine by the US, with several European countries also sending systems.
Ukraine says many more are needed to stall Russia's advance.
The US systems are M142 High Mobility Artillery Rocket System or Himars.
Crucially, the range of Himars, and many other systems, varies according to the munitions used, and it is believed that western donors have not provided the ammunition with the longest range.
The munitions thought to have been supplied to Ukraine give the system a range of about 50 miles (80km), further than the Smerch system on the Russian side.
Himars is also much more accurate than the equivalent Russian systems.
Howitzers
At the start of July, Australia, Canada and the US had also sent more than 100 M777 howitzers and 300,000 rounds of 155mm ammunition to Ukraine.
The range of the M777 is similar to Russia's Giatsint-B howitzer, and much longer than Russia's D-30 towed gun.
Ukraine's own Warsaw Pact-designed artillery uses 152mm shells.
But with stocks running low, Ukraine is shifting to the Nato-configured 155mm ammunition.
Re-orienting Ukraine's ammunition supplies is complicated and difficult, and reports suggest that Ukrainian forces are suffering a serious shortage in some areas.
Anti-tank weapons
At least 5,000 shoulder-launched Nlaw weapons, designed to destroy tanks with a single shot, have been supplied to Ukraine.
The weapons are thought to have been particularly important in stopping the advance of Russian forces on Kyiv in the hours and days following the invasion.
"Nlaw was absolutely critical to the defeat of Russian ground thrusts in the early stages of the war," according to Justin Bronk of the Royal United Services Institute.
Tanks
Ukraine has received more than 230 Warsaw Pact-designed tanks from Poland and the Czech Republic.
Ukraine's armed forces have been using T-72s for decades and have maintenance and spare parts capabilities, in addition to trained crew.
Poland's donation of tanks has been partly back-filled by alternative weaponry from allied nations, including Challenger 2 tanks from the UK.
Drones
Drones have featured heavily in the conflict so far, with many used for surveillance, targeting and heavy lift operations.
Turkey has sold Bayraktar TB2 armed drones to Ukraine in recent months, whilst the Turkish manufacturer of the system has donated drones to crowd-funding operations in support of Ukraine.
Analysts say the Bayraktar TB2s have been extremely effective, flying at about 25,000 feet (7,600m) before descending to attack Russian targets with laser-guided bombs.
They are believed to have destroyed helicopters, naval vessels and missile systems.
They have also been used to provide the exact locations of Russian positions for precision artillery strikes.
Air defences
Ukraine has successfully denied Russia full control of Ukrainian airspace during the conflict, but has called repeatedly for better air defence systems.
The US has sent NASAMS, an advanced surface-to-air missile system to Ukraine.
Kyiv has also received S-300 air defences from Slovakia.
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