If the buyer and his bank so arrange, the buyer’s bank can guarantee payment of the bill by signing the back of it. The bank’s signature is often accompanied by the words “per aval”, so that the bill is said to be “avalised” by the buyer’s bank. An avalised bill guarantees payment of the bill by the buyer’s bank if the buyer does not pay. (Instead of signing the bill, the buyer’s bank may issue a separate guarantee in respect of the bill. The effect of this is also to guarantee the payment of the bill by the buyer’s bank.)

Promissory notes can be treated in the same way. In certain countries, bills of exchange attract stamp duty: