In typography, a slab serif (also called mechanistic, square serif or Egyptian) typeface is a type of serif typeface characterized by thick, block-like serifs. Serif terminals may be either blunt and angular (Rockwell), or rounded (Courier). Slab serif typefaces generally have no bracket (feature connecting the strokes to the serifs). Some consider slab serifs to be a subset of modern serif typefaces.

Because of their bold appearance, they are most commonly used in large headlines and advertisements but are seldom used in body text. The exception is in monospaced text, many fonts for which are modeled on the typefaces used in typewriters, but that is declining in the wake of electronic publishing. Another recent exception is the typeface designed for The Guardian newspaper in the UK which is an Egyptian used through the paper as body text.

As printed material began to branch out from the familiar realm of books, new typefaces were needed for use in advertising, posters, and flyers. Slab serif printing type was first commercially introduced by Vincent Figgins under the name Antique, with copies of specimen dated 1815 and 1817.