The "Letter of the Churches of Lyons and Vienne" is an anonymous communal document from the 2nd century CE, written within the Roman Empire. It is not the work of a single author but a collective letter sent from the Christian communities in Lugdunum (modern Lyon, France) and Vienne in Roman Gaul to fellow Christians in Asia and Phrygia. The letter describes a severe persecution of local Christians, which historical sources date to around 177 CE during the reign of Emperor Marcus Aurelius.

The text is a detailed eyewitness account of mob violence, imprisonment, and the eventual execution of Christians by Roman authorities. It highlights specific martyrs, including the elderly bishop Pothinus, the slave woman Blandina, and a young man named Ponticus. The original letter does not survive independently; it is preserved in its entirety only as a quotation within the Ecclesiastical History, a 4th-century work by the church historian Eusebius of Caesarea.

According to modern scholars, the letter is a primary source of major historical importance. It provides crucial evidence for how anti-Christian persecution functioned at a local level in the Roman West before the era of empire-wide mandates. Theologically, it is considered a foundational martyr text, emphasizing themes of unwavering faith and spiritual strength. Its preservation by Eusebius ensured the story of the Lyons and Vienne martyrs became one of the most influential and celebrated accounts in early Christian tradition.