Copyediting (or monolingual editing) means checking a monolingual text in order to detect and correct errors that may have arisen in the production stage, to clarify complicated expressions, to make the text sound more idiomatic and to make its formatting and structure consistent.

Possible errors are typing mistake, grammar mistake, spelling mistake, punctuation mistake, typographical mistake, inappropriate choice of register (style), non-standard or inconsistent terminology usage, inconsistent formatting etc. Copyediting may also require further-reaching changes, which may include reorganizing sentences or paragraphs, reformatting etc.

Copyediting a text in the source language before translation usually makes the text easier to translate into the target language.