Rational actions of the additive group of complex numbers on complex n space are considered. A ring theoretic criterion for properness is given, along with ideal theoretic criteria for local triviality of such actions. The relationship between local triviality and flatness of the polynomial ring over its subring of G, invariants is investigated.

All proper rational actions of the additive group on complex affine three space admit equivariant trivializations with quotient isomorphic to complex two space. An example of an additive group action on complex seven space with a nonfinitely generated ring of invariants is presented.

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The quotient field of the ring of invariants of a rational Ga action on Cn is shown to be ruled. As a consequence, all rational Ga actions on C4 are rationally triangulable. Moreover, if an arbitrary rational Ga action on Cn is doubled to an action of Ga × Ga on C2n, then the doubled action is rationally triangulable.