It is not uncommon for regular holidaymakers to have a stash of foreign currency leftover from previous trips - with the plan of using it when they next jet abroad.
But for those who plan to use leftover Euros when they next head to Europe, some notes may soon become worthless.
The EU has spent the past few years updating its currency, which has just finished with the introduction of the new €100 and €200 notes.
Named as the Europa notes, this new currency has been phased in very gradually, beginning with €5 notes in 2013, €10 in 2014, €20 in 2015 and €50 in 2017.
New security features
This new Europa series was introduced due to its enhanced security features, which can help to guard against counterfeiting.
These security features include a new, distinct feel. The notes feature a series of short raised lines on the left and right edges, and the main image feels thicker.
The silvery stripe also reveals a portrait of Greek figure Europa inside a transparent window when tilted.
This Europa series is supposed to be more durable than the previous Euro banknotes, with the intention that they will need to be replaced less frequently.
Can I still use my old notes?
At the moment, the original series of euro banknotes can still be issued alongside the Europa series, until remaining stocks are used up.
However, once this happens they will be gradually phased out and eventually stop being legal tender.
No date for this has been confirmed as of yet, but it is reported that the European Central Bank (ECB) have said it will be announced in advance.
When the original notes cease to be legal tender, they will still retain their value, which means you will still be able to exchange them at any national central bank within the Eurosystem.
However, the ECB has decided to stop producing the €500 banknote, so there isn’t one as part of the new Europa series.
Again, this note remains legal tender, so if you do have any €500 notes leftover from previous trips, you can still use it or exchange it for smaller notes.