A specially established international committee examines new entries to the World Heritage List and decides whether the proposed sites meet the criteria defined in the World Heritage Convention on an annual basis.
The criteria of "uniqueness", of "authenticity" and "integrity" of a cultural or a natural heritage site rank among those conditions.
Together, they make up the so-called "Outstanding Universal Value" (OUV).
To assess a site's uniqueness, Unesco has developed 10 criteria, of which the first six are specifically relevant to cultural sites.
The Committee considers a property as having Outstanding Universal Value if the property meets one or more of the following criteria. Nominated properties shall therefore:
(i) represent a masterpiece of human creative genius;
(ii) exhibit an important interchange of human values, over a span of time or within a cultural area of the world, on developments in architecture or technology, monumental arts, town-planning or landscape design;
(iii) bear a unique or at least exceptional testimony to a cultural tradition or to a civilization which is living or which has disappeared;
(iv) be an outstanding example of a type of building, architectural or technological ensemble or landscape which illustrates (a) significant stage(s) in human history;
(v) be an outstanding example of a traditional human settlement, land-use, or sea-use which is representative of a culture (or cultures), or human interaction with the environment especially when it has become vulnerable under the impact of irreversible change;
(vi) be directly or tangibly associated with events or living traditions, with ideas, or with beliefs, with artistic and literary works of outstanding universal significance. (The Committee considers that this criterion should preferably be used in conjunction with other criteria);
(vii) contain superlative natural phenomena or areas of exceptional natural beauty and aesthetic importance;
(viii) be outstanding examples representing major stages of earth's history, including the record of life, significant on-going geological processes in the development of landforms, or significant geomorphic or physiographic features;
(ix) be outstanding examples representing significant on-going ecological and biological processes in the evolution and development of terrestrial, fresh water, coastal and marine ecosystems and communities of plants and animals;
(x) contain the most important and significant natural habitats for in-situ conservation of biological diversity, including those containing threatened species of Outstanding Universal Value from the point of view of science or conservation.
Operational Guidelines for the Implementation of the World Heritage Convention, Chapt. II D