Opening theory may refer to:

• Backgammon opening theory
• Chess opening theory or Chess opening theory table
• Go opening theory

• Pyromys
• Pyronaridine
• Pyronema
• Pyronemataceae
• Pyroneura
• Pyronia bathseba
• Pyronia cecelia
• Pyronia cecilia
• Pyronite
• PyRoom
• Pyropa
• Pyropelta
• Pyropelta bohlei
• Pyropelta corymba
• Pyropelta musaica
• Pyropelta oluae
• Pyropelta ryukyuensis
• Pyropelta sibuetae
• Pyropelta yamato
• Pyropeltidae
• Pyropentylene
• Pyrophaena
• Pyrophleps
• Pyrophosphate arthropathy
• Pyrophosphate ion