\
emph
does just that to its argument.
Nevertheless, typographically illiterate people (such as those that
specify double-spaced
thesis styles)
continue to require underlining of us, so LaTeX as distributed
defines an \
underline
command that applies the mathematical
‘underbar’ operation to text. This technique is not entirely
satisfactory, however: the text gets stuck into a box, and won’t break
at line end.
Two packages are available that solve this problem. The
ulem package redefines the
\
emph
command to underline its argument; the underlined text thus
produced behaves as ordinary emphasised text, and will break over the
end of a line. (The package is capable of other peculiar effects,
too: read its documentation, contained within the file itself.)
The soul package defines an \
ul
command (after which the
package is, in part, named) that underlines running text.
Beware of ulem’s default behaviour, which is to convert the
\
emph
command into an underlining command; this can be avoided by
loading the package with:
\usepackage[normalem]{ulem}Documentation of ulem is in the package itself.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=underline