The Kronecker delta, written δ_{i j} (\delta_{i\,j} in LaTeX), is a function of two variables defined as:

- δ
_{i i} = 1
- δ
_{i j} = 0 (i ≠ j)

The Kronecker delta can be defined over any set, but is usually defined on the base field of some vector space. It is commonly used in linear algebra.

The Dirac delta function is similar in some respects to the Kronecker delta, but unary and less discrete.