In hoc signo vinces

Detail from a 9th-century Byzantine manuscript. Constantine defeats Maxentius at the Milvian Bridge; the vision of Constantine is a Greek cross with ἐν τούτῳ νίκα written on it.

"In hoc signo vinces" (Classical Latin: [in ho̞ːk s̠íŋno̞ː wíŋke̞ːs̠], Ecclesiastical Latin: [in ok ˈsiɲo ˈvint͡ʃes]) is a Latin phrase conventionally translated into English as "In this sign thou shalt conquer", often also being translated as "By and/or in this sign, conquer".

The Latin phrase itself renders, rather loosely, the Greek phrase "ἐν τούτῳ νίκα", transliterated as "en toútōi níka" (Ancient Greek: [en túːtɔːi̯ níːkaː], Modern Greek: [en ˈduto ˈnika]), literally meaning "in this, conquer".