Proofreaders read printed copy or proofs to find and mark errors.

Proofreaders perform their work in two ways. Sometimes they compare proofs to the original copy and mark any differences they find. In this type of proofreading, they may use a reader to read the original copy aloud while they compare the proofs. Other times, proofreaders read the copy without anything to compare it to. In this type of proofreading, they mark errors in grammar, spelling, and punctuation. In either case, they mark copy with standard proofreader marks that are understood by writers and printers.

Proofreaders often consult reference books to do their work. This is especially true when they are reading proofs without a comparison copy. For example, proofreaders consult dictionaries for proper word usage and spelling. They consult grammar books for rules on grammar and punctuation.

Proofreaders also refer to stylebooks or style sheets used in the work place or for a specific client. A style sheet is a well-organized list of preferred usages that have no single, official rule. It includes such items as abbreviations, hyphenation, and capitalization. In some cases, proofreaders create a style sheet that follows the main style of the copy they are reading.

Proofreaders have other duties in addition to reading and marking copy. They may measure the size and spacing on the page with a printer's ruler, to be sure they are consistent.

Proofreaders mark the copy or make a list of their questions for the writer. When proofreaders finish reading and marking, they route the corrected proofs to be reprinted or reviewed.