P39 or P-39 may refer to:
- HMS P39, a United Kingdom Royal Navy submarine which saw service during the Second World War
- P-39 Airacobra, an American fighter aircraft of World War II
- Papyrus 39, a manuscript of the Gospel of John
- Phosphorus 39, one of the isotopes of phosphorus
- Fos-binding protein p39
- P39, a Latvian state regional road - see List of National Roads in Latvia
- Pier 39
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