The first shipment of Leopard 2 tanks from Germany has been sent to Ukraine, the German defence ministry says.
Eighteen cutting-edge main battle tanks were delivered after Ukrainian crews were trained to use them.
Defence Minister Boris Pistorius said he was sure the tanks could "make a decisive contribution" on the frontlines of the war.
Challenger 2 tanks from the UK have also arrived, according to reports from Ukraine.
Ukraine has been calling for more modern vehicles and weapon systems for months to help fight Russia's invasion.
The Ukrainian government is yet to comment on the arrival of the Leopard 2s, but they have confirmed the arrival of the first UK-made Challenger 2 tanks.
Around 2,000 Leopard 2s, widely regarded as being among the best main battle tanks produced by Nato countries, are in use by European countries.
Germany agreed to supply the tanks to Ukraine in January, after being initially reluctant to do so - or even to permit other countries from sending their own.
Under German law, Berlin must approve Leopard 2s being re-exported by any country.
German Defence Minister Boris Pistorius said the tanks "have made it into the hands of our Ukrainian friends as promised and on time".
The German army has trained Ukrainian tank crews to use the advanced A6 variant of the Leopard 2 over the past several weeks.
They have been specifically designed to compete with the Russian T-90 main battle tank and is considered to be easier to maintain and more fuel-efficient than most other Western tanks.
On top of the Leopard 2s, Germany has also sent Ukraine two specialist tank-recovery vehicles and 40 Marder infantry fighting vehicles.
Meanwhile, Challenger 2 tanks from the UK "are in Ukraine already", defence ministry spokeswoman Iryna Zolotar told AFP news agency.
Posting a picture of a Challenger 2 alongside other Western-made military vehicles on his Facebook page, Defence Minister Oleksii Reznikov described the British vehicle as a work of military art.
The UK Ministry of Defence declined to comment but earlier confirmed Ukrainian tank crews training in Britain had returned home after completing their training with the tanks.