Let be a countable ℵ0‐homogeneous structure. The primary motivation of this work is to study different amenability properties of (subgroups of) the automorphism group of ; the secondary motivation is to study the existence of weakly generic automorphisms of. Among others, we present sufficient conditions implying the existence of automorphism invariant probability measures on certain subsets of A and of ; we also present sufficient conditions implying that the theory of is amenable. More concretely, we show that if the set (...) of locally finite automorphisms of is dense (in particular, if has weakly generic tuples of automorphisms of arbitrary finite length), then there exists a finitely additive probability measure μ on the subsets of definable with parameters such that μ is invariant under. Moreover, if is saturated and the set of its locally finite automorphisms is dense (in particular, if is saturated and has weak generics), then the theory of is amenable. (shrink)