A typographical error (often shortened to typo), also called a misprint, is a mistake (such as a spelling or transposition error) made in the typing of printed or electronic material. Historically, this referred to mistakes in manual typesetting. The term is used of errors caused by mechanical failure or miskeying. Before the arrival of printing, the copyist's mistake or scribal error was the equivalent for manuscripts. Most typos involve simple duplication, omission, transposition, or substitution of a small number of characters.

Historically, the process of converting a manuscript to a printed document required a typesetter to copy the text and print a first "galley proof" (familiarly, "a proof"). It may contain typographical errors ("printer's errors"), as a result of human error during typesetting. Traditionally, a proofreader compares the manuscript with the corresponding typeset portion, and then marks any errors (sometimes called "line edits") using standard proofreaders' marks.

When using a typewriter, typos were commonly struck out with another character such as a strikethrough. This saved the typist the trouble of retyping the entire page to eliminate the error, but as evidence of the typo remained, it was not aesthetically pleasing. Correction fluid and correction tape were invented to hide the original mark and allow the typist to correct the error almost invisibly. There were also specialised typewriter erasers.

A more elaborate attempted solution was the "laser eraser" made by Arthur Leonard Schawlow, co-inventor of the laser. This used a laser to vaporize the ink of the typo, leaving the paper beneath unharmed. Although Schawlow received a patent for the invention, it was never produced commercially.

Later typewriters such as the IBM Correcting Selectric incorporated correction features. The development of word processors all but eliminated the need for these solutions.

In computer forums, sometimes "^H" (a visual representation of the ASCII backspace character) was used to "erase" intentional typos: "Be nice to this fool^H^H^H^Hgentleman, he's visiting from corporate HQ."

In instant messaging, users often send messages in haste and only afterward notice the typo. It is common practice to correct the typo by sending a subsequent message in which an asterisk (*) is placed before (or after) the correct word.

In formal prose, it is sometimes necessary to quote text containing typos or other doubtful words. In such cases, the author will write "[sic]" to indicate that an error was in the original quoted source rather than in the transcription.