“Variant words” (異文) refers to the different words that were used in the same or similar sentences in various version or exegeses of c1assical Chinese writtings. In the study of classical materials, variant words are some of the most important data we have. We can use them to find out the transitions in handwriting, character use, and sound borrowing (假借) of Chinese characters. We can use them to collate ancient works. More importantly, they offer new interpretations and insights to sentences in classical works. In this articleⅠwill propose a set defination for variant words, and will expound the developed background and classification of these words, in the hope that the veil of variant words can now raised.