Abstract : The group of algebraic cycles, i.e, formal sums of algebraic subvarieties of a fixed algebraic variety, is a fundamental invariant in algebraic and arithmetic geometry. Since the group is too large, we usually consider its quotients by adequate equivalence relations. Numerical equivalence is one of such equivalence relations. Its abstract definition is one of the reasons why some fundamental problems still remain. In this talk, I will explain a description of the quotient (with rational coefficients) as cohomology of some geometric object under suitable assumpt.