Syncretism /ˈsɪŋkrətɪzəm/ is the combining of different (often contradictory) beliefs, often while melding practices of various schools of thought. Syncretism may involve the merger and analogising of several originally discrete traditions, especially in the theology and mythology of religion, thus asserting an underlying unity and allowing for an inclusive approach to other faiths.

Syncretism also occurs commonly in expressions of arts and culture (known as eclecticism) as well as politics (syncretic politics).

The Oxford English Dictionary first attests the word syncretism in English in 1618. It derives from modern Latin syncretismus, drawing on Greek συγκρητισμός (synkretismos), meaning "Cretan federation."

The Greek word occurs in Plutarch's (1st century AD) essay on "Fraternal Love" in his Moralia (2.490b). He cites the example of the Cretans, who compromised and reconciled their differences and came together in alliance when faced with external dangers. "And that is their so-called Syncretism."

Giordano Bruno (1548 – February 17, 1600), (Latin: Iordanus Brunus Nolanus) born Filippo Bruno, was an Italian Dominican friar, philosopher, mathematician and astronomer. His cosmological theories went beyond the Copernican model in proposing that the Sun was essentially a star, and moreover, that the universe contained an infinite number of inhabited worlds populated by other intelligent beings. He was burned at the stake by civil authorities in 1600 after the Roman Inquisition found him guilty of heresy for his pantheism and turned him over to the state, which at that time considered heresy illegal. After his death he gained considerable fame, particularly among 19th- and early 20th-century commentators who, focusing on his astronomical beliefs, regarded him as a martyr for free thought and modern scientific ideas.

Some assessments suggest that Bruno's ideas about the universe played a smaller role in his trial than his pantheist beliefs, which differed from the interpretations and scope of God held by the Catholic Church. In addition to his cosmological writings, Bruno also wrote extensively on the art of memory, a loosely organized group of mnemonic techniques and principles. The work of Frances Yates, especially influential in anglophone scholarship, argues that Bruno was deeply influenced by the astronomy found in Arab astrology, Neoplatonism and Renaissance Hermeticism. Other recent studies of Bruno have focused on his qualitative approach to mathematics and his application of the spatial paradigms of geometry to language.