In many different fields, the complement of X is something that together with X makes a complete whole, something that supplies what X lacks.

Complement may refer to:

• complement, binary representations of negative values in computer science
• ones' complement
• two's complement

• complement (complexity), relating to decision problems and complexity classes
• complement good, a good often consumed together with another good in economics
• complement (linguistics), a word or phrase having a particular syntactic role
• complementary, a type of opposite in lexical semantics (sometimes called an antonym). See: Opposite (semantics)#Complementaries
• complement (mathematics) has many meanings — see this disambiguation page
• complementary angles, in geometry
• complement (music), an interval that when added to another spans an octave
• complementary color, in painting and optilsacs
• complementary experiments, in physics
• method of complements, a method to compute addition and subtraction in computer science
• phonetic complement
• Ship's complement, the number of persons in a ship's full company, including both commissioned officers and crew

Biology

• complement system, a cascade of proteins in the blood that form part of innate immunity
• complementary DNA, DNA reverse transcribed from a mature mRNA template
• complementarity (molecular biology), a property whereby double stranded nucleic acids pair with each other
• complementation (genetics), a test to determine if independent recessive mutant phenotypes are caused by mutations in the same gene or in different genes

See also

• Complementarity