Guillaume Adam (Latin: Guillelmus Adae), also known in English as William Adam (died ca. 1341), was a Dominican missionary, writer and French Catholic archbishop.
Adam served as the Papal missionary in Persia from 1314 to 1317, one of six Dominicans sent by Pope John XXII to Persia. However, it is now thought that Adam was probably in Persia before 1314, during the pontificate of Pope Clement V.
He was transferred to Smyrna in 1318, and served as their bishop. In 1322, he was promoted archbishop of Soltaniyeh in Persia.
On 26 October 1324, he was elected Archbishop of Antivari in the Old Doclea. He after a disagreement with the Pope, Adam stepped down as archbishop in 1341.
Directorium ad passagium faciendum, a 1332 document written in Latin that may have been authored by Guillaume Adam, testifies the existence of written Albanian at that time, although no records of written Albanian have been retrieved from before the 15th century.
- De modo Sarracenos extirpandi (ca. 1316–1317)
- Arbor caritatis