0-0
0-0 or O-O may refer to:

Emoticon for a person who wears glasses
An informal instruction to watch the conductor of an orchestra, seen in orchestral parts
Kingside castling in chess notation
Object Oriented Programming, a style of modern computer programming
A surrogate for ∞, the infinity symbol

See also
00 (disambiguation)
Zero Zero (disambiguation)
"Nothing from Nothing", a song