Abstract. In this paper we address the problem of describing in explicit algebraic terms the collective structure of the coadjoint orbits of a connected, simply connected exponential solvable Lie group G. We construct a partition p of the dual g* of the Lie algebra 9 of G into finitely many Ad*(G)-invariant algebraic sets with the following properties. For each ii e p, there is a subset X of ii which is a cross-section for the coadjoint orbits in ii and such that the natural mapping ii/Ad*(G) -► X is bicontinuous. Each Z is the image of an analytic Ad*(G)-invariant function P on ii and is an algebraic subset of 0* . The partition p has a total ordering such that for each ii € p, U{£2' : ii' < ii} is Zariski open. For each ii there is a cone W c fl* , such that ii is naturally a fiber bundle over £ with fiber W and projection P. There is a covering of I by finitely many Zariski open subsets O such that in each O , there is an explicit local trivialization 0: P-1 (O) -> W x O . Finally, we show that if ii is the minimal element of p (containing the generic orbits), then its cross-section X is a differentiable submanifold of a* . It follows that there is a dense open subset U of G~ such that U has the structure of a differentiable manifold and G~ ~ U has Plancherel measure zero.