Companies operating with in-house systems should analyse whether it is worthwhile to adjust systems to the euro or whether there is an opportunity to switch to a software package. This is one of the core provisions of the monetary law which applied to the Member States which adopted the euro at the beginning of Economic and Monetary Union. The euro became the currency of the participating Member States on 1 January 1999 and has replaced their respective national currencies. The national currencies ceased to exist, in a legal sense, as currencies in their own right. Nevertheless, as euro banknotes and coins will not be available until 2002, it must be ensured that economic agents may still use national currencies during the transition period between 1 January 1999 and 31 December 2001.
Parties are free to choose the unit they prefer in contractual relationships.
On the other hand, all acts to be performed under a contract must respect the chosen denomination - either the euro unit or the national currency unit. That means that if, for example, a contract is set up in Irish pounds all invoices and statements of accounts are to be made in pounds, unless parties agree on something different. An exception to this principle applies to payments by crediting an account. The authorisation of the account holder is not required. At the end of the transition period, by 31 December 2001, national currency units within the initial euro-zone will cease to exist.