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 Love all, a '0-0' (zero-zero) score in tennis, and less commonly in badminton Object Oriented Programming, a style of modern computer programming A surrogate for ∞, the infinity symbol
See also 00 (disambiguation) Zero Zero (disambiguation) Love All (disambiguation) "Nothing from Nothing", a song