Psi (Ψ ψ) is the 23rd letter of the Greek alphabet and has a numeric value of 700.

It has come to be a symbol for psychology-related topics, and has also been used as a shorthand for supposed psychic abilities or powers.

See also PSI (pounds per square inch).

Psi was also a character on the formerly popular game and television series, Pokémon.

The lower-case letter ψ is used as the symbol for: