Wikipedia:When to cite

The list of featured-article criteria calls for inline citations where appropriate. The English Wikipedia's Verifiability policy requires inline citations for quotations, whether using direct or indirect speech, and for material that is challenged or likely to be challenged. Editors are also advised to add in-text attribution whenever a source's words are copied or closely paraphrased. You can make clear which sources support your article using:

Material that is actually challenged by another editor requires a source or it may be removed; and anything likely to incur a reasonable challenge should be sourced to avoid disputes and to aid readers (see WP:BURDEN). In practice, this means most such statements are backed by an inline citation. In case of multiple possible references for a statement, the best reliable sources should be used.

Because the lead will usually repeat information also in the body, editors should balance the desire to avoid redundant citations in the lead with the desire to aid readers in locating sources. Leads are usually written at a greater level of generality than the body, and information in the lead section of non-controversial subjects is less likely to be challenged and less likely to require a source. There is not, however, an exception to citation requirements specific to leads. Complex, current, or controversial subjects may require many citations; others, few or none. Contentious material about living persons must always be cited, regardless of the level of generality.

The distance between material and its source is a matter of editorial judgment. The source of the material should always be clear, and editors should exercise caution when rearranging cited material to ensure that the text–source relationship isn't broken.

If you write a multi-sentence paragraph that draws on material from one source, the source need not be cited after every single sentence unless the material is particularly contentious. When multiple sources are used within a paragraph, these can be bundled into a single footnote if desired, so long as the footnote makes clear which source supports which points in the text.