The European Central Bank unveiled Tuesday the new 20-euro banknote, nine months before it starts circulating from November.
The ECB is gradually phasing in new banknotes to replace those in circulation since the euro became a physical currency in January 2002.
It started with new five-euro banknotes in May 2013 and then 10-euro notes in September 2014.
"The new 20-euro banknote will enter circulation on November 25, 2015, allowing an extended period of nine months for banknote equipment manufacturers, cash handlers and other affected parties to prepare for the new note," ECB president Mario Draghi told a news conference.
The new note will have a new security feature in the form of a "portrait window" to make it more difficult to forge.
When the banknote is held against the light, the window becomes transparent and reveals a portrait of the mythological figure Europa, visible on both sides of the note, Draghi explained.
"The portrait window is a real innovation in banknote technology," he said.
The aim was "to ensure that the euro notes continue to be resilient against counterfeiting. This will reinforce the trust that the 338 million citizens across the euro area place in their banknotes."
According to the ECB, the 20-euro note is one of the most widely used of all the euro banknote denominations, widely distributed via ATMs (automated teller machines) and accepted by many vending and ticketing machines.
The 20-euro note is to be followed, over time, by new versions of the 50-euro, 100-euro, 200-euro and 500-euro notes, the ECB said.
The central bank said there were now 17.5 billion euro banknotes in circulation in total, with a value of 1.0 trillion euros.
By the date of their November launch, the ECB will have printed more than 4.3 billion 20-euro banknotes, it said.