Traditional legislation (the "Old Approach") tended to include precise technical details within the text of the legislative document. While this made assessment against the legislation easy, it has one big drawback: unforeseen developments. A new material or novel product, that was not foreseen at the time of writing the legislation, might not fit the technical requirements. If it could not comply it would be illegal, even if perfectly safe. In order to legalise the new product, the legislation would need to be updated.

The Commission’s current workload of new legislation is such that amending existing Directives is low priority and can take decade. During this time there would be a danger of non-EU competitors stealing a lead in technological development.

To avoid this situation, the New Approach Directives now only list Essential Safety Requirements in general terms. Harmonised (ISO) standards support the technical details. As it is much easier to modify a harmonised standard then a whole directive the New Approach directives became much more practical.

New Approach directives are based on the following principles:
- Harmonisation is limited to essential requirements.
- Only products fulfilling the essential requirements may be placed on the market and put into service.
- Harmonised standards, the reference numbers of which have been published in the Official Journal and which have been transposed into national standards, are presumed to conform to the corresponding essential requirements.
- Application of harmonised standards or other technical specifications remains voluntary, and manufacturers are free to choose any technical solution that provides compliance with the essential requirements.
- Manufacturers may choose between different conformity assessment procedures provided for in the applicable directive.