Complement has a variety of uses in mathematics:

• complement, an operation that transforms an integer into its additive inverse, useful for subtracting numbers when only addition is possible, or is easier
• complement, a system for working with signed numbers in computer science
• Ones' complement
• Two's complement

• Complement graph
• Complement (group theory)
• Complement (set theory)
• Complement operator (regular expressions)
• Complementary angles
• Complementary event
• Complementary subspaces
• Complements in Boolean algebra
• Knot complement
• Orthogonal complement
• Method of complements
• Relatively complemented lattice
• Schur complement
• Complement of a point, the dilation of a point in the centroid of a given triangle, with ratio -1/2