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Sometimes I want to underline some text, and it extends past the end of a line. Why does \underline{} not automatically wrap my text for me ?

Also, how can I underline text so that it will still wrap ?

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3 Answers 3

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In text mode, the \underline command will enclose its argument in a horizontal box, which doesn't allow linebreaks. Use the \ul command of the soul package instead.

\documentclass[12pt]{article}

\usepackage{soul}

\begin{document}

A sentence that is just included to fill the line. \underline{Some text with underlining.}

A sentence that is just included to fill the line. \ul{Some text with underlining.}

\end{document}

enter image description here

EDIT: As for why \underline works the way it does, see this entry in the UK TeX FAQ for starters. It would seem that Leslie Lamport (the author of LaTeX) implemented just a "quick fix", and that only later package authors came up with more satisfactory solutions for underlining. See sections 2 and 7 of the soul documentation to get an idea of how complicated things are.

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  • This mostly answers my question, but do you also know why \underline has this behavior ?
    – gabkdlly
    Jan 24, 2011 at 10:03
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    There is also the ulem package with gives \uline. The package should be loaded with the normalem option, otherwise the \emph macro is changed to underline the text.
    – Martin Scharrer
    Apr 17, 2011 at 19:48
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    @gabkdlly: Basically \underline boxes the text using \hbox, i.e. the primitive version of \mbox. Both aren't breakable by design. The ulem package for example avoids this issue by boxing each word separately by searching for the spaces between them. This still doesn't allow for hyphenation.
    – Martin Scharrer
    Apr 17, 2011 at 19:51
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    The soul package gave me trouble when the underlined text contained cite. The ulem package worked better.
    – Vebjorn Ljosa
    Aug 15, 2012 at 21:20
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    If there is a better way to do this that is non-breaking, it should be replaced in the main environment. I am restricted on the packages I can use, therefore I cannot fix this behavior because the improvements were never backported.
    – Elliot
    Apr 22, 2013 at 18:24
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The \ul command from the soul package has troubles with Umlauts -- the \uline command from the ulem package doesn't and therefore seems to be the better option for those not exclusively writing in English.

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    One should, however, be aware that ulem doesn't support automatic hyphenation, so one has to manually hyphenate using \- with it.
    – Skillmon
    Apr 20, 2021 at 13:39
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If you're using the LuaTeX engine (or can use it) you could use the lua-ul package, that allows underlining without any restrictions on the input (unlike soul) and with fully functioning kerning, hyphenation, etc. (unlike ulem).

\documentclass[]{article}

\usepackage{lua-ul}

\begin{document}
\begin{minipage}{3cm} % to show automatic hyphenation works
  \underLine
    {%
      This is some text that gets automatically hyphenated
      while being under%
    }lined.
\end{minipage}
\end{document}

enter image description here

As you can see, hyphenation even works correctly for words not completely inside the argument of \underLine.

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