XO

XO may refer to:

• Executive officer (military)
• XO grade of cognac
• Crystal oscillator
• Tic-tac-toe (a game)
• Eastern Orthodoxy (Christianity), from the Greek: Xristianos Orthodoksos (Χριστιανός Ορθόδοξος)
• Crossover track
• XO Communications, a telecom company
• Kisses (X) and hugs (O) (may be repeated), a common postscript to a love letter