Xi
| Greek letters | |
| Α α Alpha | Β β Beta |
| Γ γ Gamma | Δ δ Delta |
| Ε ε Epsilon | Ϝ ϝ Digamma |
| Ζ ζ Zeta | Η η Eta |
| Θ θ Theta | Ι ι Iota |
| Κ κ Kappa | Λ λ Lambda |
| Μ μ Mu | Ν ν Nu |
| Ξ ξ Xi | Ο ο Omicron |
| Π π Pi | Ϻ ϻ San |
| Ϙ ϙ Qoppa | Ρ ρ Rho |
| Σ σ Sigma | Τ τ Tau |
| Υ υ Upsilon | Φ φ Phi |
| Χ χ Chi | Ψ ψ Psi |
| Ω ω Omega | Ϡ ϡ Sampi |
| Greek alphabet | |
Xi (upper case Ξ, lower case ξ) is the 14th letter of the Greek alphabet. In the system of Greek numerals it has a value of 60.
The upper-case letter Ξ is used as symbol for:
- The 'cascade particles' in particle physics.