A key article as defined by the Wikipedia:Version 1.0 Editorial Team is an article on a subject considered to be of the highest importance within its field, by experts in that field. The quality of the article has no bearing on whether or not an article is defined as "key". The subject experts would normally (but not always) be members of the appropriate WikiProject. The scope of the term "key article" is expected to grow as Wikipedia and our releases grow in size; initially it would probably encompass 10,000–20,000 articles (roughly 1% of all articles), but this may grow to perhaps 30,000 in time.

With a broad field such as history, one would expect to find perhaps several thousand key articles. With a narrower field such as History of Poland, there may be only 30 key articles, while for Polish monarchs there may only be 2 or 3 articles considered key.

The Concise Wikipedia project

Wikipedia:Concise is a project (independent of WP1.0) which aims to identify the key articles in Wikipedia. As of May 2006, around 1000 articles are grouped alphabetically, then there is a series of lists by topic.

Hierarchy of articles

The highest level in the hierarchy is concerned with articles considered to be both general and important, these are known as Core Topics. Other general articles omitted from the original list, and important articles considered essential for WP:V0.5 and subsequent releases are listed in the Core Topics Supplement. Articles considered to be the most important 1000 are listed at the next level, Vital Articles. Key articles will then make up a still broader category, perhaps the most important 1% of all articles.

Core Topics & Supplement (~ 350 articles)
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Vital Articles (~ 1000 articles)
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Key articles (10-20,000 articles)