We derive sharp Adams inequalities for the Riesz and more general Riesz-like potentials on the whole of R n . As a consequence, we obtain sharp Moser-Trudinger inequalities for the critical Sobolev spaces W α, n α (R n ), 0 < α < n. These inequalities involve fractional Laplacians, higher order gradients, general homogeneous elliptic operators with constant coefficients, and general trace type Borel measures.