The event was marked at midnight with a light display in blue and yellow, the colours of the EU, projected on its skyscraper headquarters in Frankfurt, Germany.
The introduction of notes and coins in 12 countries on January 1, 2002, was a massive logistical undertaking that followed the introduction of the euro for accounting purposes and electronic payments three years earlier.
Today, the euro is used in 19 of the 27 EU countries.
The cash introduction saw new euro notes and coins quickly replace German marks, French francs and Italian lire in ATMs, cash registers and wallets and purses.
Shop customers who paid in the old currencies received change in euros under fixed exchange rates. That swept the old currencies out of circulation as people spent their remaining national cash.
Warnings of a logistical catastrophe did not come to pass.
ECB president Christine Lagarde - in 2002 a lawyer with a global law firm - recalled withdrawing her first euros from a cash machine near her home in Normandy with friends who predicted the switch would overload the machines.
"We made a bet: if the machine gave us French francs instead of euro notes, they could keep the money," she wrote on the ECB's website.
"After midnight, we tried the cash machine. It dispensed brand new, crisp euro banknotes, and we all raised a glass to the new European currency."
The bank plans to redesign the banknotes, with a final decision on the new look expected in 2024.
The original designs with generic windows, doorways and bridges from various eras that do not represent any specific place or monument have undergone one relatively minor update since introduction.
The bank is also studying a possible digital version of the currency.
