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The Eurocodes contains choices which are open for each of the Member State to determine. These choices are named National Determined Parameters (NDP). The NDPs are published in national annexes.

A Member State does not necessarily have to choose any NDPs. In this case the choice of NDPs will be the responsibility of the designer, which must take into account the conditions of the project and the National provisions.

A National Annex is not necessary if an Eurocode Part contains no choice for NDPs or if a Part is not relevant for the Member State (e.g. seismic design for some countries).

A Member state can also choose to adopt the recommended values provided in a Eurocode part. In this case a national annex is not necessary either.

The National Annex is not a CEN requirement and has an informative status.

The National Annex contains:
- a table of contents (which must indicate in which paragraphs national choices are open and in which paragraphs national choices have been made)
- paragraphs numbered corresponding to the Eurocode, where national choices have been made.
Texts that have been changed in the National Annex are in grey and strikethrough. The new text is immediately after.

National Determined Parameters can be:

- values and/or classes where alternatives are given in the Eurocode
- values to be used where a symbol only is given in the Eurocode
- country specific data (geographical, climatic, etc.), e.g. a snow map
- the procedure to be used where alternative procedures are given in the Eurocode
- decisions on the application of informative annexes
- reference to non-contradictory

There are mainly two reasons for introducing NDPs in the Eurocode:

When the development of the ENV Eurocodes in the 90’s took place the difficulties in harmonizing all the aspects of the calculation methods was so great that “boxed values” was included. This allowed Members States to choose other values for use on their territory.

The second reason is to accommodate different safety levels in Europe.
 

Below examples on NDPs from the Eurocode are shown:

There are a great number of NDPs in the Eurocodes. The numbers differs from part to part. Below a list is shown for the most importing parts with the numbers of NDPs: