The lack of a p-adic Haar measure causes many methods of traditional representation theory to break down when applied to continuous representations of a compact p-adic Lie group G in Banach spaces over a given p-adic field K. For example, the abelian group G = Z Z p has an enormous wealth of infinite dimensional, topologically irreducible Banach space representations, as may be seen in the paper by Diarra [Dia]. We therefore address the problem of finding an additional "finiteness" condition on such representations that will lead to a reasonable theory. We introduce such a condition that we call "admissibility". We show that the category of all admissible G-representations is reasonablein fact, it is abelian and of a purely algebraic nature -by showing that it is anti-equivalent to the category of all finitely generated modules over a certain kind of completed group ringIn the first part of our paper we deal with the general functional-analytic aspects of the problem. We first consider the relationship between K-Banach spaces and compact, linearly topologized o-modules where o is the ring of integers in K. As a special case of ideas of Schikhof [Sch], we recall that there is an anti-equivalence between the category of K-Banach spaces and the category of torsionfree, linearly compact o-modules, provided one tensors the Hom-spaces in the latter category with Q. In addition we have to investigate how this functor relates certain locally convex topologies on the Hom-spaces in the two categories. This will enable us then to derive a version of this anti-equivalence with an action of a profinite group G on both sides relating K-Banach space representations of G and certain topological modules for the ringHaving established these topological results we assume that G is a compact padic Lie group and focus our attention on the Banach representations of G that correspond under the anti-equivalence to finitely generated modules over the ring. We characterize such Banach space representations intrinsically. We then show that the theory of such "admissible" representations is purely algebraic -one may "forget" about topology and instead study finitely generated modules over the noetherian ringAs an application of our methods we determine the topological irreducibility as well as the intertwining maps for representations of GL 2 (Z Z p ) obtained by induction of a continuous character from the subgroup of lower triangular matrices. Let us stress the fact that topological irreducibility for an admissible Banach space representation corresponds to the algebraic simplicity of the dual K[[G]]-module. It is indeed the latter which we will analyze. These results are a complement to the treatment of the locally analytic principal series representations studied in [ST1].