How to Comment Out Lines in LaTeX
To comment out a line in LaTeX, put a percent sign % at the start, everything after % on that line is ignored. To comment out a whole block, load \usepackage{comment} and wrap the block in \begin{comment} ... \end{comment}.
Example
% This whole line is a comment.
Visible text % trailing comment after code
\usepackage{comment}
% ...
\begin{comment}
These lines are all
ignored by LaTeX.
\end{comment}Frequently asked questions
How do I print a literal percent sign?
Escape it: write \% to show an actual % in the output, since a bare % starts a comment.
Is there a multi-line comment without a package?
You can use \iffalse ... \fi to skip a block, but the comment package (\begin{comment}...\end{comment}) is clearer and handles edge cases better.
Does a % comment also remove the line break?
Yes. A % at the end of a line eats the newline too. That is why macro definitions often end lines with % on purpose, to avoid spurious spaces in the output.
How do I comment out part of a math equation?
The same % works inside math mode: it comments out the rest of that source line. For alternatives in a derivation, copy the equation and comment out the whole old block.
Is there a keyboard shortcut to comment a block?
In most LaTeX editors (including LetX) select the lines and press Ctrl+/ (Cmd+/ on Mac) to toggle % on every selected line.
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