P9 or P-9 may refer to:

• Planet Nine, a hypothetical new planet in the far outer solar system
• Boeing XP-9, a prototype fighter aircraft from the 1930s
• Heckler & Koch P9, a semi-automatic pistol
• Springfield Armory P9, a semi-automatic pistol
• Peruvian Airlines IATA airline designator
• P9 (band), a Brazilian boyband
• Power Nine, a set of 9 rare cards from the Magic: The Gathering TCG, widely considered to be the most powerful cards ever printed in the game.
• Psyclon Nine, an aggrotech band
• P-9 Project

• 9P (disambiguation)