Abstract. Let ϕ be an analytic self-map of the unit disk. The weak compactness of the composition operators Cϕ : f → f •ϕ is characterized on the vector-valued harmonic Hardy spaces h 1 (X), and on the spaces CT (X) of vector-valued Cauchy transforms, for reflexive Banach spaces X. This provides a vector-valued analogue of results for composition operators which are due to Sarason, Shapiro and Sundberg, as well as Cima and Matheson. We also consider the operators Cϕ on certain spaces wh 1 (X) and wCT (X) of weak type by extending an alternative approach due to Bonet, Domański and Lindström. Concrete examples based on minimal prerequisites highlight the differences between h p (X) (respectively, CT (X)) and the corresponding weak spaces.