The technical definition of a conservation area is 'an area of special architectural or historic interest, the character or appearance of which it is desirable to preserve or enhance' (Planning (Listed Buildings and Conservation Areas) Act 1990.

Local planning authorities are obliged to designate as conservation areas any parts of their own area that are of special architectural or historic interest, the character and appearance of which it is desirable to preserve or enhance.
Local planning authorities also have a duty to review past designations from time to time to determine if any further parts of their area should be conservation areas.
Conservation area designation introduces a general control over the demolition of unlisted buildings and provides a basis for planning policies whose objective is to conserve all aspects of character or appearance, including landscape and public spaces, that define an area’s special interest.
There are approximately 7,000 conservation areas in England.
Conservation areas vary greatly in their nature and character. They range from the centres of historic towns and cities, through fishing and mining villages, 18th and 19th century suburbs, model housing estates, country houses set in historic parks, to historic transport links and their environs, such as stretches of canal.
The special character of these areas does not come only from the quality of their buildings. Elements such as the historic layout of roads, paths and boundaries and characteristic building and paving materials all contribute to the familiar and cherished local scene.
Designation of a conservation area gives broader protection than the listing of individual buildings. All the features, listed or otherwise, within the area, are recognised as part of its character. Conservation area designation is the means of recognising the importance of all these factors and of ensuring that planning decisions address the quality of the landscape in its broadest sense.