Abstract: Etale cohomology was introduced by Grothendieck in 1960's as a good cohomology theory that eventually enables to prove the Weil conjectures on the zeta functions of varieties over finite fields.

Taking the theory of D-modules as a model, the singular support and the characteristic cycle of an l-adic sheaf on a variety are defined recently on the cotangent bundle of the variety.

I will briefly explain the theory of characteristic cycle.