Computer Modern is the family of typefaces that Donald Knuth designed for TeX, and for decades it has been the default appearance of TeX and LaTeX documents. The design descends from the Modern (Didone) style of nineteenth-century book typography, with high contrast between thick and thin strokes and crisp serifs, which Knuth chose because it matched the look of the mathematics books he wanted to reproduce.
What sets Computer Modern apart from earlier typefaces is that it is not a single font but a parameterized program. Every character is defined in METAFONT, Knuth’s font-design language, as an outline drawn by a mathematically described pen. Because the shapes are governed by numerical parameters, the same source generates an entire coordinated family, roman, bold, italic, slanted, small caps, typewriter, sans serif, and the special math and symbol fonts, all sharing consistent proportions. Volume E of Knuth’s Computers and Typesetting series, titled Computer Modern Typefaces, gives the precise METAFONT definitions for about 500 letters, numerals, and other symbols.
The mathematical fonts are an essential part of the package, since TeX’s reason for existing was high-quality mathematics. Computer Modern supplies the italic letters, Greek characters, large operators, extensible braces and radicals, and the many sizes of symbols that formulas require, all designed to sit together harmoniously on the page. This completeness is why a TeX document full of equations looks uniform from prose to formula.
Knuth treated the fonts as a living design for a time, then froze them. On his Stanford pages he records a significant revision in spring 1992 in which “many characters were improved, notably the arrows, which now are darker and have larger arrowheads,” and he reshaped the lowercase delta he had found unattractive. Crucially, the revised characters occupy exactly the same spacing as their predecessors so that line and page breaks never change, and Knuth declared “these fonts are never going to change again.”
Because Computer Modern was originally distributed as METAFONT-generated bitmaps tied to specific resolutions, it was later converted into scalable outline formats such as PostScript Type 1 for use on modern devices and in PDF output. Derivative families, including Latin Modern, extended the original with broader language coverage while preserving its distinctive look. Computer Modern remains instantly recognizable as the typographic signature of scientific and mathematical writing produced with TeX.