ABSTRACT. Let G be a finite group acting smoothly on a homotopy sphere ~m. We wish to establish necessary and sufficient conditions for the given G-action on ~ to be topologically equivalent to a linear action. That is, we want to be able to decide whether or not there exists a G-homeomorphism y: ~ -. sm(p), where sm(p) c Rm+l(p) denotes the unit sphere in an orthogonal representation space Rm+l(p) for G. In order for a G-action on ~ to be topologically equivalent to a linear action it is clearly necessary that:(i) For each subgroup H of G the fixed-point set ~H is homeomorphic to a sphere, or empty.(ii) For any subgroups Hand H <; Hi' I .;; i .;; k, of G the pair (~Il, U7= l~Hi) is homeomorphic to a standard pair (sn, U7=lS,"i), where each Sri, I.;; i';; k, is a standard n i-subsphere of sn.In this paper we consider the case where the fixed-point set ~G is nonempty and all other fixed-point sets have dimension at least 5. In giving efficient sufficient conditions we do not need the full strength of condition (ii). We only need:(ii)' For any subgroups H and H <; Hi' I .;; i .;; p, of G such that dim ~H, = dim ~H ~ 2, the pair (~Il, U;= l~Hi) is homeomorphic to a standard pair (Sn, U;= lSin-2), where each Sr-2 , I .;; i';; p, is a standard (n ~ 2)-subsphere of sn.Our main results are then that, in the case when G is abelian, conditions (i) and (ii)' are necessary and sufficient for a given G-action on ~ to be topologically equivalent to a linear action, and in the case of an action of an arbitrary finite group the same holds under the additional assumption that any simultaneous codimension I and 2 fixed-point situation is simple. Our results generalize, for actions of finite groups, a well-known theorem of Connell, Montgomery and Yang, and are the first to also cover the case where codimension 2 fixed-point situations occur.Let G be a finite group acting smoothly on a homotopy sphere ~m. (A homotopy sphere ~m is a smooth manifold which is homeomorphic to sm.) We wish to establish necessary and sufficient conditions for the given G-action on ~ to be topologically equivalent to a linear action. That is, we want to be able to decide whether or not there exists a G-homeomorphism y: ~ --> sm(p), where sm(p) c R m + I(p) denotes the unit sphere in an orthogonal representation space Rm+ I(p) for G. In order for a given G-action on ~ to be topologically equivalent to a linear action it is clearly necessary that the following two conditions hold:(i) For each subgroup H of G the fixed-point set ~H is homeomorphic to a sphere, or empty.