Thum Ping Tjin (Chinese: ???; pinyin: Tán Bing Xin) (born 17 December 1979), also known as PJ Thum, is a Singaporean historian and former national swimmer.
He is a research fellow at the University of Oxford and the coordinator of Project Southeast Asia, a collective of scholars of Southeast Asia at the university.
The first Singaporean to swim the English Channel, he represented his country in four swim races at the 1996 Summer Olympics.