Fausto Paolo Sozzini, or simply Fausto Sozzini, was an Italian Renaissance humanist and theologian, and, alongside his uncle Lelio Sozzini, founder of the Nontrinitarian Christian belief system known as Socinianism. His doctrine was developed among the Polish Brethren in the Polish Reformed Church between the 16th and 17th centuries, and embraced by the Unitarian Church of Transylvania during the same period.

Socinianism is a Nontrinitarian Christian belief system developed and co-founded during the Protestant Reformation by the Italian Renaissance humanists and theologians Lelio Sozzini and Fausto Sozzini, uncle and nephew, respectively.