i>Yiyuan 異苑 "Garden of the extraordinary" is a collection of fantastic stories compiled during the Liu-Song period 劉宋 (420-479) by Liu Jingshu 劉敬叔 (fl. 417-426), who hailed from Pengcheng 彭城 (modern Xuzhou 徐州, Jiangsu) and was adjutant of the Inner Troops (zhongbing canjun 中兵參軍), adjutant of general Liu Daolian 劉道憐 (368-422), and finally chamberlain for attendants (langzhongling 郎中令) of general Liu Yi 劉毅 (d. 412).
Only 10 juan of the original Yiyuan have survived, but is can be assumed that not much is lost. The book includes 382 stories of strange events and supernatural appearances from ancient times to the Jin period 晉 (265-420), the latter accounting for the majority of the stories.
The literary quality of the stories differs widely. While most of them are written in a very simple and coarse language, others are more refined, like Zigushen 紫姑神 or Zhang Shen 章沉. Some of the stories were later adapted and expanded, especially by Tang-period 唐 (618-907) writers, such as the story Niuchu ran xi 牛渚燃犀 "Burning the rhino horn at Mt. Niuchu [to detect ghosts]", or some poems of Du Fu 杜甫 (712-770) that use the story Tao Kan Hunu 陶侃胡奴 "Tao Kan and his son Hunu". Some tales, like that of Zhang Hua 張華 (232-300), are written on an historical background but transgress the border to fiction, and others wholly belong to the realm of fantasy, like the story of the parrots dousing the forest fire.
The received text is a collection of fragments quoted in Song-period 宋 (960-1279) encyclopaedias like Taiping yulan 太平御覽, Taiping guangji 太平廣記 and Shilei fu zhu 事類賦注.
The Yiyuan is included in the series Tang-Song congshu 唐宋叢書, Wuchao xiaoshuo 五朝小說, Mice huihan 秘冊彙函, Jindai mishu 津逮秘書, Xuejin taoyuan 學津討原, and Siku quanshu 四庫全書.
A sequel of 10 juan called Xu yiyuan 續異苑 is mentioned in the bibliographical chapter Yiwen zhi 經籍志 of the official dynastic history Suishu 隋書.