For actions of an algebraic group scheme G on a reasonable scheme X, this paper defines a equivariant topological G-theory which compares to the algebraic K-theory of G-modules. There is a Lefschetz-Riemann-Roch theorem for the comparison map from equivariant algebraic to topological G-theory. This is an algebraic analogue of the Atiyah-Segal G-index theorem of [2], but holds for generally non-compact algebraic groups, and for possibly singular varieties in finite characteristics. It generalizes the Lefschetz-Riemann-Roch theorem for singular varieties of Baum, Fulton, and Quart [4], in that the group G need not be finite, and in that the schemes may be non-projective and in mixed characteristic.An analogue of the Segal localization or concentration theorem of [19] is proved. Combined with the Lefschetz-Riemann-Roch theorem, this yields a coherent trace formula which generalizes to possibly singular, possibly nonprojective schemes with non-finite algebraic group action the Atiyah-Bott type Woods Hole fixed point formula of [1,4,6,16].For example, let T be a torus over a field k. Let X be a scheme proper over k on which T acts. Let j: X--,Z be a T-equivariant closed immersion into a smooth T-scheme Z proper over k. Let ~ be a coherent T sheaf on X. Then the two virtual representations of T over k are equalHere X r is the fixed point scheme, @ denotes total tensor product in the derived category, and hence is the alternating sum of all the Tor's, and the division signifies multiplication by the inverse in a localization of K(T,Z r) by inverting all non-zero virtual representations over k. The key point in the proofs of these results is the strong link between algebraic geometry and algebraic topology given by my theorem in [24] 4.16, * Partially supported by NSF