  Many exponential sums over finite fields, including Gauss sums and
Kloosterman sums, arise as the Fourier transform with respect to a character of
the trace function of an $\ell$-adic sheaf on a commutative algebraic group. We
study the equidistribution of these sums when the sheaf is fixed but the
character varies over larger and larger extensions of the finite field. For the
additive group, monodromy governs equidistribution by a theorem of Deligne. A
few years ago, Katz solved the multiplicative variant of the question in a work
where Tannakian ideas play an essential role.
