To make a link in a comment you can use the `[text](url)` syntax. (And, of course, you can use simply a bare URL - but I assume you want something nicer. Having some description of a link is useful for the users reading the comment, too.) The same syntax is *possible* in posts. (Although in posts there are other possibilities how to use links. Moreover, when composing or editing a post, you can insert a link using the built-in editor.) For example, the following syntax works both in a post and in comments: `Link to a question on meta: [Hyperlink in a comment?](https://meta.mathoverflow.net/q/5410) This looks probably slightly better than a bare URL: https://meta.mathoverflow.net/q/5410` In the [first comment under this post](https://meta.mathoverflow.net/posts/comments/27526) you can see how this looks in a comment - it looks approximately like this: > Link to a question on meta: [Hyperlink in a comment?](https://meta.mathoverflow.net/q/5410) This looks probably slightly better than a bare URL: [https://meta.mathoverflow.net/q/5410 ](https://meta.mathoverflow.net/q/5410) (As [pointed out by LSpice](https://meta.mathoverflow.net/posts/comments/27542), MO links are *usually* expanded in a post to full title - so putting just `https://meta.mathoverflow.net/q/5410` in a post renders like this: https://meta.mathoverflow.net/q/5410. However, this is not true for external links - and in the comments the link to MO posts are not changed in this way either. Comments have some special links called [magic links](https://meta.stackexchange.com/tags/magic-links/info); such as `[mathoverflow.se]`, `[so]`, etc - they are expanded to a link with the full title of the site.) ----- See also: * Help center: [How do I format my posts using Markdown or HTML?](https://mathoverflow.net/help/formatting) - specifically the section "Comment formatting" * [Inline links in comments](https://meta.stackexchange.com/q/37758) (Meta Stack Exchange) * [How do you cite a reference in a comment?](https://math.meta.stackexchange.com/q/3455) and other [posts linked there](https://math.meta.stackexchange.com/questions/linked/3455) (Mathematics Meta) * [How do comments work?](https://meta.stackexchange.com/q/19756) (Meta Stack Exchange) - the section "How can I format and link in comments?" A basic information about formatting in comments is displayed after you click on "help" when you're in the window for posting a comment. (Similar screenshot can be found [in this post](https://meta.stackexchange.com/questions/24793/how-do-i-use-formatting-in-comments/77500#77500).) [![screenshot][1]][1] ---- The above concerns using (inline) links in comments. Since you have explicitly mentioned a "published article" I will add that using the [citation helper](https://meta.mathoverflow.net/tags/citation-helper/info) (in the editor) and then copy-pasting the result in a comment will not work the same way as in a post. For example, this works in a post, but [not in a comment](https://meta.mathoverflow.net/posts/comments/27539): `<cite authors="Dashiell, F. K. jun.">_Dashiell, F. K. jun._, [**Isomorphism problems for the Baire classes**](http://dx.doi.org/10.2140/pjm.1974.52.29), Pac. J. Math. 52, 29-43 (1974). [ZBL0291.46021](https://zbmath.org/?q=an:0291.46021).</cite>` However, simply removing the parts with `<cite...>` and `</cite>` yields a result which IMO [looks acceptable in a comment](https://meta.mathoverflow.net/posts/comments/27540). `_Dashiell, F. K. jun._, [**Isomorphism problems for the Baire classes**](http://dx.doi.org/10.2140/pjm.1974.52.29), Pac. J. Math. 52, 29-43 (1974). [ZBL0291.46021](https://zbmath.org/?q=an:0291.46021).` (I have used the format exactly the same as generated by the citation helper - of course, depending on personal preferences, I can imagine that some users might change it slightly.) [1]: https://i.sstatic.net/bpf8M.png