P31

• Boulton Paul P.31 Bittern, a British prototype fighter aircraft
• Curtiss XP-31 Swift, an American experimental fighter aircraft
• Percival P.31 Proctor, a British radio trainer and communications aircraft

• {{Ship|ARA|Drummond|P-31}}, a corvette of the Argentine Navy
• {{HMS|Uproar|P31}}, a submarine of the Royal Navy
• {{INS|Kavaratti|P31}}, a corvette of the Indian Navy
• {{LÉ|Eithne|P31}}, a ship of the Irish Naval Service
• {{Ship|Maltese patrol boat|P31}}, of the Armed Forces of Malta

• Makhuwa language
• Papyrus 31, a biblical manuscript
• Phosphorus-31 (P-31 or ³¹P), a stable isotope of phosphorus
• Pioneer P-31, a failed lunar probe
• P31, a state regional road in Latvia

{{Letter-NumberCombDisambig}}