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

• Melanjski Vrh
• Melankoliye
• Melankovitch Cycle
• Melanmai Ponnusamy
• Melanne Pennington
• Melanoacanthoma
• Melanoblast
• Melanoblastoma
• Melanobucco
• Melanocenchris
• Melanocercops
• Melanocercops cyclopa
• Melanocercops desiccata
• Melanocercops elaphopa
• Melanocercops ficuvorella
• Melanocercops melanommata
• Melanocercops phractopa
• Melanocetidae
• Melanocetus johnsonii
• Melanochaeta
• Melanochaeta (fly)
• Melanochaeta (fungus)
• Melanochelys
• Melanochelys tricarinata
• Melanochelys trijuga