Cash

Euro banknotes and coins are currently the only form of legal tender in Spain and other euro area countries.

Although banknotes and coins can generally be used without restrictions in cash transactions, remember that:

It is a good idea to pay with banknotes of an appropriate value for your purchase, since high-denomination banknotes may be refused when paying small amounts. •
Banks are obliged to withdraw apparently counterfeit banknotes from circulation and to identify the person they came from.
There is no obligation to accept more than 50 coins per payment, except when paying certain public sector bodies or institutions.
Cash deposited at banks should be available immediately. However, it is advisable to inform the bank in advance if you plan to deposit a large sum of money
If there is a disagreement about the exact amount of cash a customer has deposited, the cash receipt validated by the bank is the key document certifying the deposit. The electronic daily transactions listing and end-of-day cash count will also be checked.
The Banco de España will cease exchanging peseta banknotes and coins for euros on 30 June 2021.
Personal identification is necessary for transactions involving:

A cash deposit to open an account, pay for a banker’s draft or make a cash transfer.
Cash transactions for a value of €1000 or more, or a smaller amounts if the bank suspects possible money laundering or that a transaction is being divided up to avoid identification
A special declarationAbre en ventana nueva will be required when taking €10,000 or more in or out of the country, or when transporting €100,000 within the country.