Over time, policies and guidelines have developed which reflect the experience of thousands of editors who are constantly learning and refining how to create balanced, well-sourced, informative articles, and how to work with others and resolve conflict when it arises. These rules are principles, not laws, on Wikipedia. Policies and guidelines exist only as rough approximations of their underlying principles. They are not intended to provide an exact or complete definition of the principles in all circumstances. They must be understood in context, using some sense and discretion. Nevertheless there are certain things that Wikipedia is not and common mistakes that should be avoided. The five pillars is a popular summary of the most pertinent Wikipedia principles.
Core content policies
Neutral point of view
Maintaining a neutral point of view (NPOV) is one of the five pillars and founding principles of Wikipedia. This policy says that we accept all the significant viewpoints on an issue. Instead of simply stating one perspective, we try to present all relevant viewpoints without judging them. Our aim is to be informative, not persuasive. Our policy does NOT mean that our articles are expected to be 100% objective, since in any dispute all sides believe their view to be true.
Wikipedia does not achieve balance by giving all opposing points of view equal space or treating them as equally valid. Views should be represented in proportion to their representation in reliable sources. When the subject of the article is a fringe theory, such as HIV/AIDS denialism or Barack Obama citizenship conspiracy theories, the article should give much more weight to the mainstream view with the fringe view clearly described as such.
Wikipedia requires verifiable content, which means that you may only write what reliable sources have said about topics. If you cannot find reliable sources to back up your information, it cannot be included even if you think it is "true". You must cite sources for any information you contribute that is controversial or likely to be challenged, preferably by adding a footnote, as discussed in the "Citing Sources" page of this tutorial. Citations help our readers to verify what you have written and to find more information.
No original research
Wikipedia is not the place for original research — that is, facts, allegations, or ideas for which no reliable, published sources exist. This includes any analysis or synthesis of published material that serves to advance a position not advanced by the sources. Sources must support material directly and in context. For example, the statement "most computer scientists believe that P ≠ NP" must be supported by a reliable source which says that most computer scientists believe this, not by five citations of computer scientists saying that they themselves believe this without claiming to speak for the majority.
To prevent adding original research, avoid directly using primary sources if possible; instead, use secondary or tertiary sources that interpret and synthesize primary sources. Do not interpret, infer from, summarize, or synthesize primary sources yourself.
Routine calculations, translations from other languages, and faithful transcriptions of published audio and video are generally not considered original research.
The Manual of Style documents Wikipedia's house style. Its goal is to make using Wikipedia easier and more intuitive by promoting clarity and cohesion while helping editors write articles with consistent and precise language, layout, and formatting. Style and formatting should be consistent within an article, though not necessarily throughout Wikipedia. Where more than one style is acceptable, editors should not change an article from one of those styles to another without a good reason.
Wikipedia encourages an atmosphere of friendliness and openness. Of course, in practice there are sometimes disagreements and even an occasional heated argument, but members of the community are expected to behave in a generally civil manner.
The most important thing to keep in mind is that you should always assume good faith on the part of other editors. Do not assume that someone is acting out of spite or malice. If someone does something that upsets you, leave a polite message on the relevant article's talk page or on the user's talk page, and ask why. You may find that you have avoided a misunderstanding and saved yourself some embarrassment.
Wikipedia is an editable encyclopedia (along with some topics that would typically be found in an almanac). Hence, articles should consist of encyclopedic information about "notable" subjects. What exactly constitutes notability is the subject of constant debate on Wikipedia, but in no case should there be (per Wikipedia rules) an article for every person on the planet, or for every company that sells anything, or for each street in every town in the world. However, there are sister projects for certain types of non-encyclopedic content.
Encyclopedia articles are primarily about the subject, not the words for the subject, so any article that simply defines and explains the usages of a word, or short phrase, as you would find in a typical dictionary, should be contributed to the Wiktionary sister project instead.
As a general rule, do not copy and paste text from other sources. Doing so usually constitutes both a copyright violation and plagiarism. This general rule includes copying and pasting material from websites of charity or non-profit organizations, educational, scholarly and news publications, and all sources without a copyright notice. If a work does not have a copyright notice, assume it to be under copyright-protection. Brief quotations of copyrighted text may be used to illustrate a point, establish context, or attribute a point of view or idea. Use of copyrighted text must be in compliance with Wikipedia:Non-free content criteria policy.
Note: To view this information in an article style format, see contributing to Wikipedia. Wikipedia also has "topic specific tutorials"; and The Wikipedia Adventure a comprehensive and fun 7-mission interactive guided tour, which covers all the essentials about editing and the expectations and norms of the Wikipedia community.