C0 or C00 has several uses including:

• C0, the IATA code for Centralwings airline
• C0 and C1 control codes
• a CPU power state in the Advanced Configuration and Power Interface
• an alternate name for crt0, a library used in the startup of a C program
• in mathematics:
  • the differentiability class C⁰
  • a C₀-semigroup, a strongly continuous one-parameter semigroup
  • c₀, the Banach space of real sequences that converge to zero
  • a C₀ field is an algebraically closed field
• in physics, c₀, the speed of light in vacuum
• %C0, the URL-encoded version of the character "À"
• C0, a note-octave in music
• an ISO 216 paper format size
• C00, the ICD-10 code for oral cancer
• C° could refer to:
  • An abbreviation for Celsius degrees
  • In chemistry, the standard state for solute concentration

• CO (disambiguation), the two letter combination