I have been fascinated with typographic ligatures for quite some time. Ligatures are a class of glyphs composed of two individual letters. There are two classes, historical and stylistic ligatures. Historical ligatures were present since the beginning of scripts, possibly to increase writing speed. Stylistic ligatures occurred more “recently”, with the invention of (analog) printing. The computer typesetting system TeX supported ligatures since its beginning in the 1980s. Other software, such as Word, introduced them much later.
Examples of historical ligatures
There are a myriad of historical ligatures in modern European languages. However, many people are not aware of them. For example, the German Umlauts ä, ö, and ü are ligatures. The two dots arose from superscript e. The circumflex in French (e.g. ô) originates from an s in Latin that became silent. Cedilla (fr. cédille, e.g. ç), also called hook or tail, is a subscript z. The name literally means ‘little z’. There are many more examples in modern European and other languages, not necessarily originating from Latin or Germanic.
In TeX/LaTeX, typesetting these historical ligatures involves either the inputenc package or the backslash escape character (i.e. ‘\’). The first lets you type many special characters directly.
\documentclass{article}
\usepackage[utf8]{inputenc}
\begin{document}
% Inputenc package
ö, ä, ü, é, ê, ç
%Manually
\"o, \"a, \"u, \'e, \^e, \c{c}
\end{document}
It is important that the option used is the same as the tex file encoding, here utf8.
Examples of stylistic ligatures
Stylistic ligatures include f + adjacent letter (e.g. fi, fl, or ff) or the ampersand (i.e. &, see below). TeX produces f-ligatures by default. For example, notice the elongated hood of the (first) f in fi and ff:
\documentclass{article}
\begin{document}
% Default ligatures and ampersand
ff, fi, fl, \&
\end{document}
Note, the ampersand is a reserved character in LaTeX (e.g. for tabular column separation) and has to be escaped in any case.
For a comprehensive list of escapable characters see: The Comprehensive LaTeX Symbol List.
The ampersand: &
The ampersand, or &, is a stylistic ligatures, which originates from the Latin word et, meaning and. In other words, & is a ligature, which combines e and t. This becomes evident when typesetting ampersand in italics, e.g. using Computer Modern or Libre Caslon fonts:
\documentclass[border=5]{standalone}
\usepackage[T1]{fontenc}
\usepackage{librecaslon}
\begin{document}
{\fontfamily{cmr}\selectfont{\itshape\&}\par}{\itshape\&}
\end{document}
To finish, a fun fact about ampersand: The word ampersand is a corruption of the phrase “and (&) per se (means) and”.
Source Wikipedia: Typographic Ligatures and Ampersand.