Yintong is a working prototype of a full-scale database of characters in the Guǎngyùn 廣韻, a major dictionary dating from 1008 C.E. All data was entered into the database by me and I am responsible for any necessary corrections in future. Yīntōng has been endorsed by the T‘ang Studies Society and a mirror site is now being set up at the American Oriental Society, where future development may take place. At present, the database has the following basic functions: 1.If a character is entered, return information about the fǎnqiè associated with the character, the phonological values represented by those fǎnqiè, the page number of the Guǎngyùn where that reading appears. 2.If a medieval Chinese reading is entered (in various forms), return a list of the other characters in the same xiǎoyùn. 3.If two medieval Chinese readings are entered, return a list of any characters appearing in both xiǎoyùn. 4.If a piece of Chinese text is entered, return a transcription of each character based on the Guǎngyùn’s readings.