Greek letters

Greek letters are entered inside math mode as commands such as \alpha and \beta. Three things are worth fixing in your mind: almost every lowercase letter has a command; uppercase letters have a command only when their shape differs from a Latin capital; and some letters come in two glyph shapes (variants), such as \epsilon versus \varepsilon. This page sorts out how to enter them, gathers the lowercase, uppercase, and variant forms into lookup tables, and closes with how to get upright and bold Greek.

How Greek letters are entered

Greek letters are symbols used inside math mode. Writing \alpha straight into the body (text mode) is an error, so you enter math mode first, as in $\alpha$. The command names are just the English spellings of the letters — \alpha, \beta, \gamma, and so on. The letter that comes out is set in math italic (slanted), like any variable.

角度 $\theta$ と波長 $\lambda$ を使う。
\[
  E = \hbar \omega, \qquad \Delta x \, \Delta p \ge \frac{\hbar}{2}
\]

Here \theta, \lambda, and \omega are lowercase, while \Delta is uppercase (the command name starts with a capital). Command names are case-sensitive, so \Delta (Δ) and \delta (δ) are entirely different letters. These all work in standard LaTeX, but a few variants such as \digamma and \varkappa need the amssymb package (covered below).

Before the tables, hold on to the three points from the start. (1) Every lowercase letter except omicron has a command. (2) Uppercase letters whose shape matches a Latin capital (Α, Β, Ε …) have no command — you type the Latin letter instead. (3) Several letters have variant-shape commands (\var…). We take each in turn.

Lowercase letters

For the lowercase letters, every one of the 24 except omicron has a command. Omicron shares its shape with the Latin lowercase o, so it has no dedicated command — you simply type o in math mode. The table below is the full lowercase set (the glyph is the real character; the reading is given in Japanese / English).

In the table above, the shapes of \epsilon and \phi (ϵ, ϕ) have alternative forms too, covered in the “Variant forms” section next. Also, \xi (xi) and \zeta (zeta), and \nu (nu) versus \upsilon (upsilon) versus \mu (mu), are easy to confuse by eye — rely on the command name in the source so you do not mix them up.

Uppercase (the key point)

This is where Greek trips people up most. LaTeX provides a command for an uppercase Greek letter only when its shape differs from a Latin capital. Capital gamma Γ is a shape Latin does not have, so \Gamma exists; but capital alpha looks exactly like A, so **there is no \Alpha command**. When you want a capital alpha, you just type A in math mode.

Commands exist for just these eleven letters: \Gamma, \Delta, \Theta, \Lambda, \Xi, \Pi, \Sigma, \Upsilon, \Phi, \Psi, \Omega. In math they are set upright, in contrast to the slanted lowercase letters.

The remaining capitals — alpha, beta, epsilon, zeta, eta, iota, kappa, mu, nu, omicron, rho, tau, chi — are typed as the matching Latin capitals A B E Z H I K M N O P T X. One caveat, though: a Latin letter typed in math mode is set as a variable in italic (math italic), so these “Greek capitals” come out slanted, not upright. Be aware that this clashes with the upright look of the eleven \Gamma-type letters (to make them all upright, use upgreek, in the next section).

% 命令のある大文字（立体）
\[ \Gamma(n) = (n-1)!, \qquad \sum \to \Sigma, \qquad \Omega = \mathrm{V/A} \]
% 命令のない大文字はラテン文字を直接（数式中では斜体になる）
\[ A = \pi r^2 \quad (\text{ここで } A \text{ は大文字アルファのつもり}) \]

Variant forms

Even for one letter, printing tradition and field conventions sometimes use two glyph shapes. LaTeX distinguishes them with separate commands, giving the variant a name prefixed with var (variant). Epsilon, for instance, has the rounded \epsilon (ϵ) and the lunate \varepsilon (ε), and mathematics tends to prefer the latter, ε. Which you pick is a matter of look and convention, not meaning — the rule of thumb is to be consistent within a document.

A few practical pointers. In mathematics many people choose \varepsilon (ε) for epsilon, and physics often uses \varphi (φ) for phi. \varpi (ϖ) resembles omega, so watch out for confusion. \varsigma (ς) is the sigma that appears at the end of a Greek word and is rarely used in formulas. And **only \varkappa (ϰ) and \digamma (ϝ) are undefined in standard LaTeX** — they require \usepackage{amssymb} in the preamble. There are no var… variants on the uppercase side (uppercase variant shapes such as \varGamma belong to a separate mechanism, covered under math fonts).

Upright and bold Greek

By default, lowercase Greek letters are set slanted, as variables. But sometimes you want a Greek letter for a constant, a unit, or a symbol that should be upright rather than for a quantity. The classic case is the constant π: the ISO rules for mathematical typesetting prescribe that mathematical constants are upright (roman), so the constant π should properly be set as an upright π (standard LaTeX \pi is slanted).

To get upright Greek, the **upgreek package** is handy. With \usepackage{upgreek} loaded, lowercase letters become \upalpha, \upbeta, \uppi, \upmu, … and uppercase become \Upgamma, \Updelta, … — up-prefixed commands that yield the upright shape. Use it, for example, for the “micro” unit μ, or to set the constant π upright.

\usepackage{upgreek}
% ...
% 定数 π は立体で（ISO 規則）
\[ C = 2 \uppi r \]
% 変数なら斜体のまま
\[ \pi \text{（角度の変数など）} \]

For bold Greek letters (vectors, tensors, and the like), use \boldsymbol{…} from amsmath/amsbsy, or \bm{…} from the bm package. Writing \boldsymbol{\alpha} or \bm{\omega} gives the bold (boldface italic) math symbol. \mathbf{…} works on Latin letters but often has no effect on lowercase Greek, so \boldsymbol/\bm is the standard choice for Greek. The full picture of choosing math typefaces is covered under “Math fonts.”

In short: standard commands (slanted) for Greek used as quantities; upgreek’s \up… for things that should be upright, such as constants and units; and \boldsymbol/\bm when you want bold. For the conventions on when to use slanted, upright, and bold, see also “ISO/JIS math typesetting rules.”