P4
P4 may refer to:

Computing
 Intel Pentium 4, a 7th-generation processor design
 The P4 power connector introduced to power it and later CPUs in the ATX12V 1.0 standard
 The i486DX (P4) model of the Intel 80486, a high-performance microprocessor
 P4 (programming language), for describing packet forwarding
 P4, the Perforce software command line client

Media
 P4 Radio Hele Norge (PFI), a Norwegian radio company
 Kanal 24 (Kanal 4), which acquired the Norwegian P4 channel from PFI
 Sveriges Radio P4, a Swedish radio channel
 Persona 4, a 2008 video game
 Periphery IV: Hail Stan, 2019 album by American progressive metal band Periphery

Military
 Skaraborg Regiment (armoured), a Swedish army unit whose designation is P 4
 Peugeot P4, a vehicle used by the French Military

Science
 P4 laboratory, a biosafety level 4 facility
 Tetraphosphorus (P4), an allotrope of phosphorus
 Group p4, the plane symmetry group Wallpaper group p4
 Progesterone (Pregn-4-ene-3,20-dione), a steroid hormone
 Kerberos, the fourth moon of Pluto
 Perfect fourth, an interval in music theory
 Enterobacteria phage P4
 P4, an EEG electrode site according to the 10-20 system
 P4 cell, a stage in the Caenorhabditis elegans embryonic development

Roads
 P4 road (Latvia)
 P04 road (Ukraine)

Other uses
 Papyrus 4, a New Testament manuscript
 Trans-Pacific Strategic Economic Partnership, or P4, a free trade agreement between Brunei, Chile, New Zealand, and Singapore
 Protofour, or P4, a set of standards for model railways

See also
 4P (disambiguation)
 Phosphate, molecular formula PO43−.
 Play (telecommunications) P4, Polish cellular telecommunications provider