Let Fr be free group of rank r > l and O u t F r = A u t Fr/InnFr, the outer au tomorph ism group (automorphisms modulo inner automorphisms). We shall prove the following. Theorem. The maximum order of a f ini te subgroup G of Out F, is 12, for r= 2, and 2 r r !, for r > 2. Furthermore the f inite subgroup of Out F, realizing the maximum order is unique up to conjugacy, for r > 3. The proof of the above theorem is based on the following geometric realization result which was observed first in [Z, p. 478], see also [Cu]. Proposition 0 Let G be a .finite subgroup of Out F,. Then there exist a f inite connected graph F with ~ 1 F = F , and an action of G on F realizing the given action on F,. Remarks and definitions. Let F' be a subgraph obtained by deleting all free edges of F, i.e., edges with vertex of valence 1. Note that the G action restricts on the new graph F ' and the fundamental g roup and the induced action on it do not change. So we may assume in Proposi t ion 0 that F contains no vertex of valence 1. We use Sym F to denote the symmetry group of F (in a combina tor ial sense, i.e., mapping vertices to vertices and oriented edges to oriented edges, or equivalently, homeomorph i sms acting linearly on edges). In general we allow inversions of edges, i.e., reflections in the midpoints of edges (which is not considered as the identity). Then, in Proposi t ion 0, we may also assume that F has no vertices of valence 2 by amalgamat ing the two adjacent edges containing the same vertex of valence 2 into one edge, again G acts on the new graph with the same induced action on the fundamenta l group. We say that a g roup G acts effectively on F if it can be embedded into Sym F, or equivalently, no non-trivial element of G is the identity on F. For a connected graph F, its rank, denoted by rank F, is the rank of its fundamental group. Lemma 1 Let F be a connected graph of rank r > 1 without vertices of valence 1 and G be a f ini te group acting on F. Then G acts effectively on F if and only if the induced action on ~ F injects into Out ~ F.