Isaiah Pseudo is the name given to the unknown author of an early Christian text, The Ascension of Isaiah, which was likely compiled in the late first or early second century CE. The author's identity and life are completely unknown. According to modern scholars, the work probably originated within a Jewish-Christian community, possibly in Syria or Palestine, as it combines Jewish apocalyptic themes with early Christian beliefs about Jesus.

The author's only known work is The Ascension of Isaiah (also called the Martyrdom and Ascension of Isaiah). It is a pseudepigraphical text, meaning it was attributed to the prophet Isaiah but not actually written by him. The full text survives in an Ethiopic translation, with fragments existing in Greek, Latin, and other ancient languages. It is a composite narrative detailing the prophet Isaiah's martyrdom and his visionary journey through the seven heavens.

The text is significant as a key source for understanding early Jewish-Christian theology. It provides early evidence for developing ideas about the pre-existence of Christ and his descent through the heavens, concepts that would shape later Christian doctrine. The detailed cosmology and focus on prophecy and martyrdom offer scholars valuable insights into the beliefs and literary practices of early Christian communities.