The last set of eyes before publication, catching typos, formatting errors, and anything that slipped through earlier editing rounds.
A proofreader reviews the final, formatted version of your book and catches the small errors that survived every previous round of editing. They're looking at the text after it's been typeset or formatted for publication, which means they also check for layout issues like orphaned lines, inconsistent spacing, missing page numbers, and formatting glitches. They are not rewriting sentences or questioning plot choices. Their job is narrow and precise: make sure nothing embarrassing makes it to print.
You've spent months or years writing your book, and nothing undermines a reader's confidence faster than a typo on page three. Proofreading is your last safety net. It's also where errors introduced during the formatting and typesetting process get caught, things that didn't exist in your manuscript file but crept in during production. Skipping this step is how books end up with missing words, duplicated paragraphs, and broken formatting.
A proofreading failure for the ages. The word 'not' was accidentally omitted from the Seventh Commandment, printing 'Thou shalt commit adultery.' The printers were fined and most copies destroyed.
Early copies contained a handful of typos and errors that were corrected in later printings. Those uncorrected first editions are now worth thousands to collectors.
Norris details the proofreading process at The New Yorker, where multiple proofreaders read every piece and the standards are famously exacting.
Print out a chapter of your work (physical paper, not a screen) and read it backwards, sentence by sentence, starting from the last sentence. This strips away narrative flow and forces you to see each sentence in isolation. Mark every typo, missing word, or punctuation error you find. This technique is borrowed from professional proofreaders.