Book excerpt: In recent decades, the Tang dynasty (618-907) has acquired a reputation as the most 'cosmopolitan' period in Chinese history. The standard narrative also claims that this cosmopolitan openness faded after the An Lushan Rebellion of 755-763, to be replaced by xenophobic hostility toward all things foreign. This Element reassesses the cosmopolitanism-to-xenophobia narrative and presents a more empirically-grounded and nuanced interpretation of the Tang empire's foreign relations after 755.