Iota in LaTeX (\iota)

Where it is used

Lowercase Greek iota, a dotless narrow letter used for inclusion maps and index notation.

\iota commonly names an inclusion or embedding map, as in \iota : A \hookrightarrow X, and the interior product \iota_X \omega in differential geometry. APL and some functional languages use iota for an index generator, which shows up in computer science writing. Because it resembles a dotless i, make sure it is not confused with \imath, the dotless i used under accents. There is no \Iota command; capital iota looks like Latin I. It is rare enough that a one-line definition the first time you use it helps readers.

Minimal compilable example

Paste this into an empty .tex file and compile it with pdfLaTeX, XeLaTeX or LuaLaTeX.

\documentclass{article}
\begin{document}
Iota: $\iota$

\[ \iota : A \hookrightarrow X, \quad \iota(a) = a \]
\end{document}

Related symbols

• Kappa\kappa
• Theta (Upper)\Theta
• Lambda\lambda
• Theta\theta
• Lambda (Upper)\Lambda
• Eta\eta

Frequently asked questions

How do I write Iota in LaTeX?

Type \iota in math mode, for example $\iota : A \hookrightarrow X, \quad \iota(a) = a$. It works in plain LaTeX without loading any package.

Which package do I need for \iota?

None. \iota is part of standard LaTeX, so it compiles with nothing in the preamble but the document class.

Can I use \iota in text mode, or only in math mode?

Only in math mode. Outside $...$ LaTeX stops with "Missing $ inserted", so write $\iota$ in running text. If you only need the glyph in text, paste the Unicode character ι instead (with XeLaTeX or LuaLaTeX and a font that has it).